Preheat oven to 400 degrees F.
Lightly drizzle with olive oil a 9×13 baking dish.
Add melted butter, lemon juice, zest, minced garlic, pepper flakes, dried parsley, salt, and pepper in a medium bowl. Whisk to combine.
Wash the fish fillets, pat dry with paper towels, and season with salt and pepper on both sides. Arrange them on the bottom of the prepared baking dish slightly overlapping.
Drizzle with the lemon butter mixture, top with capers and lemon slices.
Transfer to the preheated oven and bake for about 10-12 minutes, or until fish flakes easily with a fork.
Garnish with chopped parsley and serve immediately.
