No boil tuna noodle casserole is every bit as creamy as you would want it to be, but with almost no prep. Just layer everything in the pan and let the oven do the work for you!
Layer half of the uncooked noodles on the bottom of the pan.
Distribute the tuna, peas, and mushrooms over the noodles. Top with the remaining noodles.
In a bowl, mix together the water, cream, sour cream, mustard, salt and pepper.
Pour the liquid ingredients over the noodles in the casserole dish. Cover tightly with foil and bake for 40 minutes.
Uncover the casserole and sprinkle with cheese. Bake uncovered for an additional 10-15 minutes. The sauce should be thickened, cheese melted, and noodles cooked. Let sit for a few minutes before serving.