Preheat your oven to 350°F (175°C).
In a large skillet, heat the avocado oil over medium heat. Add the diced yellow onion and minced garlic, sautéing until fragrant and translucent, about 3-4 minutes. Add the breakfast sausage to the skillet, breaking it apart with a spatula. Cook until browned and cooked through, about 5-7 minutes.
Once the sausage is cooked, add the diced red bell pepper and chopped baby spinach to the skillet. Season with sea salt and black pepper. Sauté for another 3-4 minutes, until the spinach wilts down and the bell pepper softens.
In a large mixing bowl, whisk together the eggs, cottage cheese, and all-purpose flour until smooth.
Add the sautéed sausage and vegetable mixture into the egg mixture, stirring gently until combined. Fold in the grated colby jack cheese and half of the chopped green onions.
Pour the mixture into a greased 9x13 inch baking dish and bake for 35-40 minutes or until the top is golden brown and a toothpick inserted in the center comes out clean.
Once baked, remove the casserole from the oven and allow it to cool for a few minutes. Garnish with the remaining chopped green onions before slicing and serving.