It may be a bit of a stretch to call this dish a casserole — it's not baked and it's not made in a traditional casserole dish — but that's what I grew up calling it. This no-bake tuna casserole was a staple in my house growing up (and it's still a favorite to this day), and it's the epitome of comfort food. Noodles, cheese, green peas, and tuna — doesn't get much easier (or delicious!) than that. I've made this version a tiny bit healthier by subbing in whole-grain penne and nonfat milk, but feel free to go for full-on comfort food if you want!
In a large pot over high heat, boil enough water for pasta. Salt the water and cook the pasta according to the package directions. When the pasta has 4 minutes left to cook, add the frozen peas. Drain the pasta and peas when cooked.
Return the pasta and peas to the pot over low heat. Add the milk and stir. Add the tuna and stir to combine. Working slowly, stir in the shredded cheese until it is incorporated. Serve immediately.