Preheat the oven to 375 degrees F (190 degrees F). Grease a 9x13-inch baking dish.
Place tilapia fillets in the bottom of the baking dish, then dot with butter and season with garlic salt and seafood seasoning.
Top each fillet with a slice or two of lemon.
Arrange frozen mixed vegetables around fillets and season lightly with salt and pepper. Cover the dish with aluminum foil.
Bake in the preheated oven until vegetables are tender and fish flakes easily with a fork, 25 to 30 minutes.
Serve hot and enjoy!