Make the Cream of Mushroom Soup (recipe here https://lifecurrentsblog.com/homemade-cream-of-mushroom-soup/ ).
While soup simmers bring a large pot of salted water to a boil and cook pasta, cooking pasta for 1 minute less than the package instructions (pasta will continue to cook in the oven). Drain pasta, reserving about ½ cup of cooking water.
Stir cream of mushroom soup, salt, pepper, frozen peas, and ½ cup of shredded mozzarella together. Mix in the pasta. Mix in 2 tablespoons of pasta cooking water. If mixture seems too thick, or if you’re making casserole a day before for leftovers, stir in additional pasta cooking water 1 tablespoon at a time until desired consistency is reached. Taste for salt and pepper.
Place mixture in a casserole dish, and sprinkle remaining ½ cup shredded mozzarella over the top.
Bake casserole, uncovered, in 375 degree oven for 20-25 minutes, or until cheese is bubbly and browned a bit.
Notes
Casserole can be made a day in advance and kept in the fridge for tomorrow's lunch or dinner.