What is a common cheese for omelette?
What is a good filling for an omelette?
Sautéed asparagus, avocado, pea shoots, and feta or goat cheese (pictured here)

Sautéed spinach, sautéed mushrooms, and Swiss cheese.
Diced bell peppers, onion, and cheddar cheese.
Roasted tomatoes, basil, and fresh mozzarella.