Cook vegetables and sausage: In a medium nonstick skillet, heat butter or oil over medium heat. Add onion and bell pepper and sauté for 2–3 minutes until softened. Add mushrooms and sliced sausage. Cook for another 4–5 minutes, stirring occasionally, until browned and cooked through.

Pour in the beaten eggs and swirl to coat the pan evenly. When nearly set, add the cheese and fold the omelet in half.

Serve the omelet topped with a sprinkle of grated Parmesan cheese, with fruit and orange juice.