Cut onion, bell peppers and cabbage into 1-inch squares. Cut carrots on diagonal into thin slices. Chop 3 cloves of garlic and crush remaining clove through press. Cut green beans into 1 1/2-inch pieces. Combine soy sauce and brown sugar. Heat oil in a large deep skillet. Stir-fry onion over high heat for 2 to 3 minutes, until browned around the edges. Add carrot, bell pepper, chopped garlic, ginger and pepper flakes and stir-fry 2 minutes. Add cabbage and stir-fry until slightly wilted, 3-5 minutes. Add broccoli, cauliflower, and 1 1/2 cups of the broth. Bring to a boil, cover and cook, stirring occasional, 5 to 7 minutes. Menawhile, in a small bowl combine peanut butter, remaining broth, soy sauce mixture, lemon juice, sugar and crushed garlic. Stir into stew and simmer uncovered, for 5 minutes. Serve in chopped peanuts and scallions sprinkled on top.