Steam cauliflower in microwave with 1 cup water for ~3 minutes until tender.
Drain and pat dry.
Preheat oven to 400°F (200°C). Lightly grease a 13×9-inch baking dish.
In a skillet, cook sausage over medium-high heat for ~15 minutes. Drain and set aside.
In the same skillet, heat olive oil.
Sauté mushrooms for ~10 minutes until liquid is gone.
In a large bowl, combine cauliflower, sausage, mushrooms, and green pepper. Toss to mix.
See full steps with tips & photos → https://theboatshedcafe.com/low-carb-pizza-casserole/