Preheat an oven to 375 degrees F (190 degrees C); prepare a baking dish with cooking spray.

Combine the butter, lemon juice, and garlic in a microwave-safe bowl; heat in microwave in 10-second increments until the butter is completely melted and the garlic has softened, stirring between each session, about 1 minute total.

Arrange the tilapia in the bottom of the prepared baking dish; pour the butter mixture over the fillets assuring they are all evenly covered. Sprinkle the parsley over the tilapia.

Bake in the preheated oven, turning the fillets every 10 minutes, until the fish flakes easily with a fork, about 40 minutes total.