In cup, with fork, stir garlic, lemon peel, salt, and pepper until well blended; use to rub on both sides of steak.
In a nonstick 12-inch skillet, heat oil over medium heat until very hot. Add steaks and cook 5-6 minutes per side for medium-rare or until desired doneness. Transfer steaks to plate, keep warm.
In cup, blend cornstarch and broth until smooth. In same skillet, add broth mixture,tomatoes, and spinach. Heat to boiling over medium-high heat; cook, stirring until spinach wilts, 1-2 minutes. Cut each steak in half and serve with spinach mixture.