Step 1: Preheat the oven to 400°F. Season fish fillets with the salt and pepper and use your hands to rub the seasoning into the fish. Dice the onion.
Step 2: Place a small skillet over low heat. Add oil and onion. Sauté for 1 minute. Transfer the sautéed onion to a square 8x8-inch baking dish.
Step 3: Add the fish fillets to the baking dish and season with granulated sun-dried tomatoes, Nigella seeds, and oregano.
Step 4: Add the peeled tomatoes to the baking dish, sprinkle lightly with salt and pepper (if desired), and place in the oven.
Step 5: Bake for 25 minutes, until fish fillets are cooked through. Remove from the oven and let cool for 5 minutes. Just before serving, sprinkle generously with parsley.
Notes
*Nigella seeds, also known as black cumin, can be omitted and instead use an additional ¼ teaspoon black pepper.