Step 1

Place oven racks in upper and lower thirds of oven. Preheat to 425 degrees F. Line one large baking sheet with parchment paper.

Step 2

Place cauliflower in a food processor. Process until finely grated. Transfer to a microwave-safe bowl. Cover loosely and microwave on High for 3 minutes. Let cool slightly. Transfer the cauliflower to a clean kitchen towel and wring out excess moisture. Return to the bowl and stir in Cheddar, egg, pepper and salt until thoroughly combined. Using about 1/4 cup of the cauliflower mixture for each, create eight 3-inch squares on the prepared baking sheet.

Step 3

Toss pepper and onion with oil on a large rimmed baking sheet. Bake the cauliflower squares and the vegetables, switching the pans in the oven halfway through, until the cauliflower is browned and crispy around the edges and the vegetables are soft, 20 to 25 minutes.

Step 4

Lightly oil a large nonstick skillet; heat over medium heat. Chop the peppers and onions. Place about 1/4 cup pepper mixture and a slice of cheese on one cauliflower "toast." Top with a second cauliflower "toast." Repeat with the remaining cauliflower toasts, vegetables and cheese. Cook, turning once, until the cheese is melted, about 4 minutes total.