1. Prepare pasta according to package directions. Three minutes before the pasta is done, stir in the broccoli or cauliflower. Drain pasta and vegetables and transfer to a large bowl.
2. In a small bowl, dissolve the cornstarch in 1/4 cup of water. Put the garlic in a large saucepan with chicken broth. Simmer over medium heat for 3 minutes. Whisk in the cornstarch. Stir in the the mixed vegetables and spinach and cook until hot, about 5 minutes.
3. Toss the sauce and vegetables with the pasta, season with salt and pepper and sprinkle with Parmesan cheese and serve.