In a large skillet, cook bacon until crisp; remove to paper towels to drain. Discard drippings. In the same skillet, stir-fry beef in 1 tablespoon oil until no longer pink, about 2 minutes. Remove beef and pan juices; keep warm.
In the same skillet, saute the broccoli, cauliflower, carrot, onion and ginger in remaining oil for 3 minutes. Add the mushrooms, water chestnuts and garlic; cook and stir 2 minutes longer. Dissolve bouillon in boiling water; stir into vegetables.
Stir in soy sauce and beef with pan juices. Combine cornstarch and cold water until smooth; add to the pan. Bring to a boil; cook and stir for 1-2 minutes or until thickened. Stir in bacon and spaghetti.