Combine the five spice powder and 3 tablespoons soy sauce in a small bowl. Pour over the steak. Leave the steak mixture out while preparing the rest of the ingredients.
Chop the onion, celery, green pepper, and red pepper.
Heat a large skillet or wok over medium-high heat. Add the beef and marinade. Brown on all sides. Remove the beef from the pan.
Add the onion, celery, green pepper, red pepper, water chestnuts, and beef broth to the pan, stirring and cooking for 5-10 minutes until tender. Return the beef to the skillet and add the remaining 1 tablespoon soy sauce. Cook until thoroughly heated. If desired, serve over brown rice and top with cashews.