1. Preheat your oven to 375 degrees F (190 degrees C).
2. In a mixing bowl, combine cream of mushroom soup, milk, garlic powder and black pepper. Stir until smooth.
3. Add the drained tuna, chopped onion and frozen peas to the soup mixture and mix well.
4. Spread frozen fries in an even layer in a 9×13-inch baking dish.
5. Pour the tuna mixture evenly over the fries.
6. Sprinkle the top with grated cheddar cheese.
7. Bake in the preheated oven for about 25 to 30 minutes, or until the fries are golden brown and the cheese is bubbling.
8. Let cool for a few minutes before serving.
Variations and tips
To meet different tastes, you can try replacing the cream of mushroom soup with cream of chicken or cream of celery. For a touch of cheese, add cream cheese or substitute mozzarella for the cheddar for a milder flavor. If your family likes it spicy, add some chopped jalapeños or sprinkle with red pepper flakes before cooking. For those who prefer a lighter version, replace some fries with slices of zucchini or add more vegetables like corn or peppers.