This Slow Cooker Mongolian Flank Steak is the kind of bold, saucy comfort food that’s perfect for busy weeknights.

Tender strips of beef are simmered in a sweet-savory garlic soy sauce until melt-in-your-mouth soft, then served over fluffy rice for a dish that feels like takeout—but better.

Whether you’re feeding the family or craving something cozy with minimal effort, this crockpot Mongolian beef delivers big flavor with almost no prep.

Why You’ll Love This Recipe

Effortless slow cooker meal – Just mix, pour, and let it cook.

Tender and flavorful – Flank steak becomes fork-tender in a rich, sticky sauce.

Better-than-takeout taste – Sweet, salty, and slightly spicy in every bite.

Great with rice or noodles – Perfect for soaking up all that delicious sauce.

Make-ahead friendly – Leftovers are just as tasty the next day.

What You’ll Need (Ingredient Highlights)

For the Beef

Flank steak – Lean, flavorful, and ideal for slow cooking.

Cornstarch – Helps thicken the sauce and coat the beef for better texture.

For the Sauce

Soy sauce – The salty, umami-rich base.

Brown sugar – Adds sweetness and creates that signature glossy finish.

Garlic powder – A pantry shortcut for depth.

Sesame oil – Infuses the sauce with nutty aroma.

Onion – Adds savory depth and softens as it cooks.

Red pepper flakes – Just a hint of heat (adjust to taste).

Pro Tips Before You Start

Slice against the grain – After cooking, slice the flank steak across the grain for extra tenderness.

Don’t skip the cornstarch – It thickens the sauce and gives it that classic Mongolian-style texture.

Use low-sodium soy sauce – Helps balance the sweetness and saltiness.

Make it spicier – Add more red pepper flakes or a splash of sriracha.

Serve with sticky rice or noodles – Great for soaking up that savory-sweet sauce.

How to Make Slow Cooker Mongolian Flank Steak

Step 1: Make the Sauce

In a mixing bowl, whisk together: ¼ cup cornstarch, 2 Tbsp sesame oil, ½ tsp garlic powder, ½ cup soy sauce, ¾ cup brown sugar, 1 diced onion, ¼ tsp red pepper flakes

Mix until smooth and fully combined.

Step 2: Add to the Slow Cooker

Place 1.5 lbs flank steak in the bottom of a 6-quart slow cooker.

Pour the sauce mixture over the meat, ensuring it’s fully coated.

Step 3: Let It Cook

Cover and cook on:

LOW for 6–8 hours, or

HIGH for 3–4 hours

The beef should be extremely tender and infused with flavor.

Step 4: Slice or Shred

Once cooked, remove the steak and slice against the grain into strips, or shred if preferred.

Return the meat to the slow cooker to soak in the sauce for another 5–10 minutes.

Step 5: Serve and Enjoy

Spoon the beef and sauce over steamed white rice, brown rice, or noodles.

Garnish with sliced green onions or toasted sesame seeds, if desired.

What to Serve With Mongolian Flank Steak

Steamed jasmine or basmati rice – Classic and perfect for soaking up sauce

Garlic green beans – Light and crisp contrast

Simple cucumber salad – Refreshing and cool

Fried rice or lo mein – For a full takeout-style spread

Asian-style slaw – Crunchy and zesty on the side

Variations and Substitutions

Swap the beef – Use skirt steak, sirloin, or even sliced chuck roast.

Add veggies – Toss in bell peppers or broccoli during the last hour of cooking.

Use fresh garlic and ginger – For even more bold flavor.

Go gluten-free – Use tamari or coconut aminos instead of soy sauce.

Want it low carb? – Serve over cauliflower rice or zucchini noodles.

Storage Tips

Fridge – Store leftovers in an airtight container for up to 4 days.

Freezer – Freeze cooked beef and sauce in portions for up to 2 months.

Reheat – Warm gently on the stovetop or in the microwave. Add a splash of broth if needed.

FAQs

Can I prep this the night before?
Yes! Mix the sauce and add it to the slow cooker with the beef.

Cover and refrigerate, then cook the next day.

Does flank steak get tender in a slow cooker?
Absolutely. It becomes fall-apart tender after hours of slow cooking.

Can I thicken the sauce more?
If needed, stir in a cornstarch slurry (1 Tbsp cornstarch + 1 Tbsp water) at the end and cook on high for 10–15 minutes.

Can I make this spicy Mongolian beef?
Yes! Add more red pepper flakes, or stir in chili garlic sauce or sriracha.

Can I cook this on the stovetop instead?
This recipe is tailored for slow cooking.

For stovetop, use a sliced beef stir-fry method instead.

Final Thoughts

This Slow Cooker Mongolian Flank Steak is everything you love about takeout—sweet, salty, savory, and ultra-saucy—but made right in your kitchen with just a handful of pantry ingredients.

It’s tender, flavorful, and perfect for a fuss-free dinner that feels fancy with almost no effort.

Don’t forget the rice and extra napkins—this one’s a saucy favorite you’ll want to make again and again.