- Preheat grill to medium. Mash chopped garlic and kosher salt together on a cutting board using the flat of a chef’s knife or a spoon until combination forms a thick paste.
- Transfer garlic paste to a small bowl, add olive oil, and mix. Coat suitable length of aluminum foil with oil or cooking spray. Place the salmon fillet skin-side down on the foil, then spread garlic paste on top of salmon.
- Sprinkle with 1/3 cup sliced basil, lay sliced tomatoes on top (for an extra-nice touch, overlap them to look like fish scales), and add salt and pepper to taste.
- Place salmon and foil on grill and cook until fish flakes easily, about 10–12 minutes. Use two large spatulas to transfer salmon from foil to serving platter, and garnish with remaining 1/4 cup of sliced basil.