An easy weeknight casserole you can make ahead and keep in fridge until ready to cook.
Preheat oven to 350 degrees.
Cook pasta according to package directions.
In a small saucepan, saute onions and mushrooms in butter.
Remove from heat and add peas, tuna, mushroom soup, milk, mustard, and lemon juice.
Pour cooked noodles into a large casserole dish and add the vegetable/tuna mixture.
Gently combine everything together.
Top evenly with cheese.
Bake in the oven about 30 minutes until cheese is bubbly.