Combine vinegar, tamari, ginger and garlic in a medium bowl. Toss sliced beef in mixture and marinate in the refrigerator for 30 minutes.
After beef has marinated, heat a large skillet over medium-high heat. Add beef and marinade and cook until beef is just done to your liking, about 5 minutes. Remove beef and juices to a bowl, cover and keep warm.
Add ½ cup water to the skillet, bring to a simmer, add onions and cook 3 minutes or until tender.
Stir in bell peppers, green beans, and carrots. Reduce heat to medium and cover. Cook until vegetables are just fork tender, 7 to 8 minutes, stirring once.
Uncover and increase heat to medium-high and cook for about 2 minutes longer. Return beef and any juices to skillet and cook 1 minute longer to heat everything thoroughly.
Serve with cooked brown rice and garnish with cashews.