1. Preheat oven to 400 degrees.
2. Heat a large ovenproof skillet over high heat. Add 1 tablespoon oil to the skillet and swirl to coat. Sprinkle the fillets with 1/2 teaspoon salt and 1/4 teaspoon pepper. Add the fillets, skin-side down, to the skillet and sauté for 2 minutes. Place the skillet in the oven until the salmon is the desired degree of doneness, about 3 minutes for medium-rare and up to 8 minutes for well-done, depending on the thickness of your salmon fillets.
3. Heat a large cast-iron skillet over medium heat. Add the remaining 2 tablespoons oil to the skillet and swirl to coat. Add the garlic and cook for 2 minutes or until lightly browned, stirring occasionally. Increase the heat to medium-high. Add the tomatoes to the skillet and sauté for 2 minutes or until the skins blister, stirring frequently. Remove the skillet from the heat. Sprinkle the remaining 1/4 teaspoon salt, remaining 1/4 teaspoon pepper, basil, and shallots over the tomato mixture and toss to combine. Spoon the tomato mixture over or alongside the salmon.
Enjoy!