Preheat oven to 175°C while cooking noodles

In a pan, melt butter and cook onion on low until soft.

In a large bowl, mix soup + milk until smooth. Add tuna, peas, onion, salt, pepper, and cooked noodles. Mix well

Stir in half the cheese

Pour into a baking dish, top with remaining cheese

Bake 25–30 minutes until hot and bubbly