Add the oil to a nonstick pan and cook the chicken sausage until nicely browned. Add the onions and bell peppers. Sauté for about 3 - 4 minutes until softened.

Add the Eggs: Pour the eggs over the cooked vegetables and sausage in the pan. Allow it to cook undisturbed for about 1 - 2 minutes until the edges begin to set.

Using a spatula, gently lift the edges of the omelet and tilt the pan to allow any uncooked egg to flow to the edges. Cook for another 2 - 3 minutes until the eggs are fully set but still moist. Add the cheese to the omelet and fold it over. Cook until the cheese it melted. Top with sliced avocado.