Pre-heat oven to 350 degrees F. Lightly grease an 8x8 casserole dish with cooking spray and set aside.
Cook pasta according to package instructions. Drain and set aside.
In a large pot, melt the butter and whisk in the flour. Whisk for 1-2 minutes over medium heat. Adjust heat if needed to avoid burning.
Slowly whisk in the milk. Continue whisking and allow the sauce to thicken-slightly simmering-for about 2 minutes over medium-low heat.
Once sauce has slightly thickened add the cheeses (reserving ½ cup of the cheddar jack for topping). Whisk till all cheese is melted. Gently stir in the pasta, peas, tuna and mushrooms. Season with salt and pepper.
Top with crushed potato chips. Bake 25-30 minutes.