Heat oil in a 10-in. nonstick ovenproof skillet over medium-high heat. Add onion and peppers, and cook, stirring often, until softened, 8 to 10 minutes. Add cherry tomatoes, and cook, stirring occasionally, until tomatoes begin to burst, 3 to 4 minutes. Add egg mixture and cook, stirring gently, until eggs just begin to set and vegetables are evenly distributed, about 30 seconds to one minute.