Heat oven to 425°F. Line a baking sheet with foil; coat with cooking spray. Divide pizza dough into 4 equal pieces. Working directly on prepared baking sheet, flatten each piece into a 6-inch circle with a thick edge. Bake 7 minutes.
In small bowl, combine tomato sauce, oregano,and garlic powder; set aside. In another small bowl, combine mozzarella and cheddar cheeses.
In small skillet, heat oil over medium-high heat. Add onion and bell pepper; cook 3 minutes, stirring occasionally, until vegetables are crisp-tender.
Spoon 2 tablespoons of sauce onto each crust; top with 1/4 cup cheese, 1/4 of the vegetable mixture, and 1/4 of the tomato slices.