2. Heat the olive oil in a large skillet over medium heat. Add the onion and cook, stirring occasionally, until it is soft and translucent, about 5 minutes. Add the garlic and artichokes, season with salt and pepper, cook for 2 more minutes and transfer to a baking dish.
3. Season the rockfish fillets with rosemary, salt and pepper and place them in the baking dish. Pour the tomatoes over the fillets and sprinkle with lemon juice, salt and pepper. Bake until the fish is just cooked through, about 10 to 12 minutes, depending on the thickness of the fish.