1. Toss beef with garlic and oil. Set aside.
2. Cook pasta according to package directions, adding spinach to water during last 3 minutes of cooking. Drain well.
3. While pasta is cooking, heat a large nonstick skillet over medium-high heat. Stir-fry beef until outside is seared and no pink remains.
4. Drain excess fat from the pan and add the tomatoes. Cook over medium-high heat until sauce is thickened. Add pasta to sauce, toss to coat. Cook until heating through, then serve hot, garnished with cheese.