Preheat the oven to 350˚. Coat a 10-inch ovenproof nonstick saute pan with the olive oil. Add the sausage and cook over medium heat until browned, 3 to 4 minutes. Add the bell peppers and sauté until tender, about 5 more minutes.
Whisk the eggs and 1/4 cup water in a large bowl. Add the cheese and season lightly with salt. Using a heatproof rubber spatula, stir the eggs into the pan with the sausage and peppers until evenly distributed. Cook the frittata until the eggs are set on the bottom and around the sides of the pan, about 4 minutes.
Place the pan in the oven and bake until the eggs are cooked through, about 15 minutes. Remove the frittata from the pan and cut into wedges. Serve hot or at room temperature.