Preheat your oven to 425°F and line a baking sheet with parchment paper.
Rice the cauliflower by pulsing in a food processor until it resembles coarse crumbs. Transfer the riced cauliflower to a microwave-safe bowl, cover, and microwave for 5-7 minutes until softened.
Once the cauliflower is cool enough, place it in a clean towel and squeeze out excess moisture.
In a mixing bowl, combine the cauliflower, beaten egg, salt, and pepper. Mix thoroughly until the mixture binds.
Spread the cauliflower mixture evenly onto the prepared baking sheet, shaping it into a thin round crust.
Bake the crust in the preheated oven for about 15-18 minutes until the edges become crispy and golden.
Remove the crust from the oven and spread a thin layer of tomato sauce over it.
Sprinkle the shredded mozzarella evenly over the sauce.
Top with sliced bell pepper, fresh spinach, and cherry tomatoes. Drizzle olive oil lightly over the vegetables and add a pinch of salt and pepper.
Return the pizza to the oven and bake for an additional 5-7 minutes until the cheese melts and the vegetables are slightly roasted.
Remove from the oven, let cool for a few minutes, slice, and serve.