Preheat the oven to 375 degrees f.
Heat the oil in a cast iron (oven safe) skillet, then add onion, sweet peppers, garlic, and chili and saute for about 5 minutes, until the veggies soften a bit.
Add the tomatoes, olives, balsamic vinegar and season with salt and pepper to your taste.
Cover and simmer for 5 minutes, then add the cod fillets, nestling them evenly into the sauce.
Cook in the preheated oven for 12-15 minutes, or until fish is cooked through and flakes easily.
Garnish with fresh chopped parsley and enjoy!