Boil pasta in lightly salted water for 10 minutes, or until al dente; drain well. Return the pasta to the pot it was cooked in.
Preheat oven to 180 degrees C. Spray a 2 1/2 litre casserole dish with cooking spray.
Mix tuna with cream of mushroom soup, cream of celery soup, milk, salt, black pepper and garlic in a medium saucepan. Place pan over medium low heat and heat through. Alternatively, place these ingredients in a microwave safe dish and warm in the microwave.
Mix tuna mixture with pasta. Spread 1/2 of the noodles into the prepared dish. Arrange the cheese slices over the noodles, then spread the remaining noodle mixture over the cheese. Top with crushed potato chips.
Bake, uncovered, for 20 to 30 minutes; cook until the casserole is hot and the chips begin to brown. Let cool for 10 minutes before serving.