Rinse the fish, pat it dry with a paper towel, and make a few cuts on the skin. Season with salt, drizzle with olive oil, and place a few rosemary sprigs inside the cavity. Cook on the grill or bake in the oven until done. For extra flavor, add chili for heat, fennel seeds for spice, or mint for freshness. You can also substitute rosemary with thyme or oregano. Serve with a side of creamy mashed potatoes.