Tuna and Mashed Potato Casserole: Comfort Food with a Savory Twist

Preheat your oven to 375°F (190°C). Lightly grease a 9×9-inch casserole dish with butter or non-stick spray.
Prepare the filling:

In a large bowl, combine the mashed potatoes, drained tuna, peas (if using), chopped onion, mayonnaise, milk, garlic powder, and dried thyme. Stir until everything is well mixed. Taste and season with salt and pepper to your preference.
Assemble the casserole:

Spoon the tuna and mashed potato mixture into the prepared casserole dish, spreading it evenly. If you like, sprinkle the shredded cheddar cheese on top for an extra layer of flavor and a golden crust when baked.
Bake the casserole:

Place the casserole in the preheated oven and bake for 20-25 minutes, or until the top is lightly golden and bubbly.
Serve:

Once baked, remove the casserole from the oven and let it cool for a few minutes before serving. Enjoy it as a standalone dish or paired with a simple green salad for added freshness.
Serving and Storage Tips: