Season the chicken with garlic powder, onion powder, 1/8 teaspoon salt, and black pepper. Set aside.
Bring 2 frying pans sprayed with non-stick spray to medium heat on the stove. In one pan, cook bell pepper, mushrooms, and onion until softened, 4 to 6 minutes.
In the other pan, cook chicken until cooked through, about 3 minutes per side.
Cook's Note: Alternatively, use one frying pan and cook the veggies and chicken consecutively.
Place crushed tomatoes in a small bowl and season to taste with garlic powder, onion powder, salt, and pepper. Evenly spoon seasoned tomatoes onto chicken in the pan. Tear string cheese into pieces and place over the tomatoes.
Top chicken with vegetables and turkey pepperoni. Cover with a lid and continue to cook until the cheese softens, 1 to 2 minutes.
Plate your pizza-fied chicken and sprinkle with grated topping. Garnish with crushed red pepper and oregano, if using. Enjoy!
PER SERVING: 282 calories, 5.75g fat, 868mg sodium, 10g carbs, 2g fiber, 4.5g sugars, 44g protein