Preheat the oven to 350°F. Combine the softened butter, minced garlic, salt, pepper, fresh herbs, and lemon zest in a small mixing bowl until fully incorporated. Lightly grease a 3L baking dish with cooking spray and arrange the fish fillets in a single layer. Generously spread the prepared butter mixture over each fillet and top with thin lemon slices. Bake for 15–20 minutes or until the fish flakes effortlessly with a fork.