Heat oven to 350 degrees. Whisk eggs and season with salt and pepper. Stir in tomato sauce.
Heat an 8-inch skillet over medium-low heat. Brush with olive oil. Pour in egg mixture and cook until edges begin to set, 2 to 3 minutes.
Arrange shells in egg mixture and cover with foil. Transfer to oven and bake until just set in the middle, 20 to 22 minutes.