Preheat oven to 400 degrees.
Combine cream of mushroom soup, milk, tuna (drained), salt and black pepper as preferred, grated Parmesan cheese, 1/2 cup chopped onions (if using), frozen peas, and cooked noodles in a 3-quart casserole. Stir until evenly combined
Sprinkle shredded cheddar cheese evenly over top.
Bake for 30 minutes OR until bubbling hot and cheese has melted.
Carefully remove from hot oven.
Sprinkle top with French fried onions.
Return to oven and bake 5 more minutes OR until French fried onions are golden brown.
Watch closely to prevent burning.
Sprinkle each serving with grated Parmesan cheese (optional).
Pour leftovers in a container. Seal shut with lid or foil. Store in refrigerator.