Preheat an indoor or outdoor grill to medium-high. Heat the oil in a skillet set over medium heat. Add the shallots and garlic and cook until fragrant, about 1 to 2 minutes. Add the tomatoes and stock, bring to a simmer. Simmer until the tomato softens and starts to fall apart and form a chunky sauce, about 10 minutes. Season with salt and pepper, then reserve over low heat.
Season the steaks with the salt and pepper. Grill to the desired doneness, allowing 3 to 4 minutes per side for rare to medium-rare. Stir the chopped basil into the tomato sauce. Spoon an equal amount onto four dinner plates. Set the steaks on the sauce, garnish with fresh basil leaves and serve