Preheat oven to 350 degrees F. Drizzle 1 teaspoon olive oil on bottom of a baking dish (8x8 or 9x13) and layer in shallot and garlic. Place cod on top of garlic and shallot and season all over with 2 teaspoons salt and black pepper as desired. In an alternating pattern, layer sliced citrus on top of fish (keeping the halved lemon separate).
Drizzle olive oil on top of cod and citrus until fully coated. Transfer to preheated oven and roast until fish is cooked through and opaque, 30-40 minutes (depending on thickness of the fish).
While the fish bakes, make harissa vinaigrette: In a medium bowl, combine harissa, juice of ½ lemon (save remaining half for another use), honey, 1 tablespoon olive oil, ¼ teaspoon salt, and pepper as desired. Whisk to combine.
Once fish has finished roasting, garnish with chopped parsley. Serve directly out of baking dish, and drizzle harissa vinaigrette over top. Keep leftovers refrigerated in an airtight container for 2 to 3 days.
Photography and styling by Julia Gartland