Cook pasta according to package directions; add frozen vegetables to cooking water just to thaw. Drain; place mixture in a 2-quart casserole dish that has been sprayed with non-stick vegetable spray.
Mix sour cream, milk, one cup cheese, ham, onion and garlic; stir into pasta mixture in dish.
Bake, uncovered, at 350 degrees for 30 minutes. Sprinkle with croutons and remaining cheese during last 5 minutes of baking.