In a large skillet, heat olive oil over medium-high heat. Add sausage; cook, stirring occasionally, until browned, about 5 minutes. Using a slotted spoon, remove sausage from pan; let drain on paper towels. Add bell peppers and onion to skillet. Cook, stirring occasionally, until just tender, about 5 minutes. Using a slotted spoon, remove peppers and onion, reserving drippings in skillet. Arrange sausage and pepper mixture over pizzas. Bake 8 minutes.