Pulse cauliflower florets in a food processor until chopped into rice-sized pieces. Transfer riced cauliflower to a microwave-safe bowl.
Preheat the oven to 350 degrees F (175 degrees C). Coat a 7x11-inch baking dish with cooking spray.
Warm a skillet over medium heat. Add red and green bell pepper, onion, jalapeno pepper, chili powder, and cumin. Cook, stirring every 2 minutes, until peppers are soft and roasted, 5 to 10 minutes. Remove from heat.
Cook cauliflower rice in the microwave for 3 minutes. Stir in tomatoes and 1 cup shredded Cheddar cheese. Add bell pepper mixture and stir to combine.
Spread cauliflower mixture into the prepared baking dish. Top casserole with remaining Cheddar cheese.
Bake casserole in the preheated oven until melted, 30 to 35 minutes.
