Preheat your oven to 425°F.
Rice the cauliflower by pulsing florets in a food processor until fine. Transfer to a microwave-safe bowl and microwave for 5 minutes until softened.
Let the cauliflower cool slightly, then transfer to a clean towel and squeeze out excess moisture. Combine the cauliflower with the egg, mozzarella, parmesan, and a pinch of salt to form a dough.
Spread the cauliflower mixture onto a parchment-lined baking sheet forming a thin, even crust. Bake in the preheated oven for 15-20 minutes until the edges start to crisp.
While the crust bakes, season the chicken breast with salt, pepper, and mixed Italian herbs. In a small pan, heat olive oil and sear the chicken until cooked through, about 4-5 minutes per side, then slice into strips.
Chop the red bell pepper, red onion, and zucchini. Toss with a little olive oil, salt, and herbs. Roast in the oven alongside the crust for about 10-12 minutes until tender.
Remove the crust from the oven and spread the tomato sauce evenly over it. Arrange the sliced chicken and roasted vegetables on top.
Return the pizza to the oven for an additional 5 minutes to heat through and allow the flavors to meld.
Remove from the oven, slice, and serve immediately.