Preheat the oven to 375°F (190°C) and lightly spray a 3x13 baking dish.
Heat a skillet over medium heat, add olive oil, pinch of salt, and sauté the diced onion and bell peppers for 3–4 minutes until softened.
Add the sausage and cook until browned and fully cooked through. If using pre-cooked sausage, sauté just to warm them up with the vegetables. Set aside.
In a bowl, whisk the eggs and then stir in the cottage cheese, cheddar cheese, sausage, bell peppers, onions, salt, and pepper.
Pour the egg mixture in the baking dish.
Bake in the preheated oven for about 30-35 minutes or until the casserole is set and lightly browned on top.
Once done, remove from the oven and let it cool for a few minutes before slicing and serving.