Preheat oven to 400°F. Lightly grease a 9×13 baking dish with cooking spray.
Add tilapia in an even layer on bottom of dish and season with salt, pepper, oregano, and paprika. Set aside.
In a small bowl, whisk melted butter, lemon juice, and minced garlic.
Pour evenly over each fillet. Top each fillet with 1-2 lemon slices.
Bake for 12-14 minutes, or until tilapia is tender and flakes easily. Spoon additional sauce from dish over each fillet and serve immediately.