1. Bring a large pot of salted water to a boil and preheat the oven to 425°F.
2. Once boiling, add egg noodles and cook for 5 to 8 minutes, slightly less than package instructions.
3. Once the noodles are almost cooked, drain them, and place them in a large bowl along with the soup, tuna, half the cheese, peas, mushrooms, and onion.
4. Stir everything together in the large bowl until well combined.
5. Once combined, transfer the mixture to a lightly greased baking dish, lightly coated with the non-fat cooking spray, and top it with the remaining cheese.
6. Then, place the baking dish in the hot oven to cook for 15 to 20 minutes.
7. After that time, remove the baking dish from the oven and let cool slightly.
8. Once cooled, you can either dig in and enjoy it right away, or divide it evenly into 5 air-tight containers and store in the fridge!
9. If storing in the fridge, simply heat up a serving in the microwave when ready to enjoy.
