Combine hoisin, ginger, garlic, bitter orange, soy sauce, sesame seeds, ground oregano and adobo in medium bowl and pour over beef.
Make sure beef is completely covered with marinade and marinate in a covered bowl for a minimum of 30 minutes.
Cut green and red bell peppers in thin strips, and put aside. Peel and chop onion into thin wheels.
Heat a large pan on medium low heat. Pour in 2 tbsp of oil, add vegetables and stir.
Pour 1 tbsp of vinegar over the vegetables. Mix well and saute until tender. Remove from pan and set aside.
Use remaining 2 tbsp of oil back in pan or wok. Increase heat to medium high and add marinated beef.
Pour 4-5 cups of water to the liquid where the meat was marinating. Increase heat to high. Whenever the liquid in the pan dries, add 1 or 2 cooking spoonfuls of the marinating liquid. This prevent the meat from burning.
Continue to stir fry beef until fully cooked and pour onions & peppers mixture over beef, cook for 1 minute.