Using a sharp knife, cut the fish into 6–7 oz fillets—slightly larger than a deck of playing cards.
Place the fish in a bowl and add the sliced garlic and shallots. Drizzle generously with 1-2 tbsp of extra virgin olive oil, and season with a hefty pinch of kosher salt. Toss gently to coat.
Add 2 layers of parchment paper to your braiser, or wide pan. Pour in the crushed tomatoes, then nestle in the cod, shallots, and garlic.
Add the chopped anchovies, capers, both types of olives, dried oregano, and a pinch of chili flakes if using them.
Place the lid on the pot, folding the parchment paper inward. Simmer over medium-low heat, fully covered, for 15–20 minutes. Cook time will vary depending on the thickness of the fish. Check at the 15 minute mark, the fish should be completely cooked through and easily flake with a fork.