Method:

Preheat the Oven: Preheat your oven to 180°C (350°F).

Prepare the Fish: If using whole mackerel, rinse them under cold water and pat dry with paper towels. Make a few diagonal slashes on both sides of each fish to help absorb the flavors.

Season the Fish: Place each fish on a large sheet of parchment paper or foil. Stuff the belly of each fish with lemon slices, crushed garlic, rosemary, and parsley. Drizzle with a bit of olive oil and season with salt and pepper.

Wrap the Fish: Fold the paper or foil around the fish, ensuring it's tightly sealed, but leave a little room for the steam to circulate inside the packet. This will keep the fish juicy and tender as it bakes.

Bake the Fish: Place the wrapped fish on a baking sheet and bake in the preheated oven for about 25-30 minutes, or until the fish is cooked through (check for flakiness). If you're using thicker fish, you might need to adjust the cooking time.

Serve: Carefully open the packet at the table to release the delicious aromas, and serve with a simple side of roasted vegetables or a fresh salad.

Variations and Tips:

Herbs: You can experiment with different herbs like basil or dill, depending on your preference.

Other Fish: While mackerel is traditional, you can substitute it with other fish such as sea bass, snapper, or trout.

Vegetables: Add thinly sliced potatoes or cherry tomatoes into the packet for extra flavor.

Substitutions for Dietary Needs:

Gluten-Free: This recipe is naturally gluten-free.

Dairy-Free: It is also dairy-free.

Vegetarian: For a vegetarian version, you can substitute the fish with hearty vegetables like zucchini, eggplant, or mushrooms.