Directions

1. In a medium bowl, whisk eggs with 1/2 teaspoon salt and 1/4 teaspoon pepper; set aside. In a 10-inch nonstick skillet with a tight-fitting lid, heat 1 tablespoon oil over medium-high. Add bell peppers and onion; season with salt and pepper. Cook, stirring frequently, until softened, 6 to 8 minutes.
2. Add eggs, and cook, quickly stirring with a heatproof rubber spatula, until eggs thicken, about 1 minute. Sprinkle cheese evenly over egg mixture. Cover skillet; reduce heat to medium-low. Cook frittata for 15 minutes. Remove skillet from heat, and let stand, covered, 5 minutes.
3. Meanwhile, whisk together vinegar and remaining 2 tablespoons oil in a large bowl; season dressing with salt and pepper. Add lettuce, and toss to combine.
4. Slide frittata onto a work surface; cut into wedges. Top frittata with salsa, and serve with salad.