Preheat the oven to 350°F (175°C).
Cook the egg noodles in a large pot of boiling salted water according to package instructions until al dente. Drain and set aside.
In a large skillet, melt the butter over medium heat.
Add the chopped onion and cook for 4-5 minutes until softened.
Add the minced garlic and chopped jalapeño to the skillet and cook for an additional 1-2 minutes, stirring frequently.
In a large mixing bowl, combine the cream of mushroom soup, whole milk, and shredded cheddar cheese. Stir until smooth.
Add the cooked noodles, sautéed onion, garlic, jalapeño mixture, flaked tuna, thawed peas, salt, and black pepper to the bowl. Gently fold everything together until well combined.
Transfer the mixture to a 9×13-inch baking dish and spread evenly.
Sprinkle the crushed potato chips evenly over the top of the casserole.
Bake in the preheated oven for 25-30 minutes, or until the casserole is bubbly and the topping is golden brown.
Remove from the oven and let it rest for 5 minutes before serving.