Preheat the oven to 400°F (200°C)
Line a baking sheet or dish with parchment paper or lightly grease it
Pat the flounder fillets dry with paper towels
Place the fillets on the prepared baking sheet
Brush or drizzle the fillets with olive oil or melted butter
Season with salt, black pepper, garlic powder, and paprika if desired
Add lemon slices or a squeeze of lemon juice
Bake for 10 to 15 minutes, depending on thickness
Check that the fish flakes easily with a fork and is opaque
Remove from the oven and serve immediately