In a bowl, add slices of beef with soy sauce, cornstarch, oyster sauce and vegetable oil. Mix everything together and let it stir for at least 15 minutes.
In an another bowl, mix beef broth or chicken together, oyster sauce, soy sauce, sugar, cornstarch and sesame oil. Keep it aside.
In a large skillet, heat a tablespoon of vegetable oil over high heat. Put the marinated beef and cook until it is thoroughly cooked. Remove the beef from the skillet and keep it aside.
In the similar skillet, put another tablespoon of vegetable oil. Add the garlic, onion, ginger and stir-fry for around until fragrant, it may take around 1-2 minutes.
Add bell peppers, celery and snow peas and stir-fry for more 3-4 minutes until the veggies are crispy and tender.
Add water chestnutes, bean sprouts, bamoboo shoots, mushrooms and let them stir fry for 2 more minutes.
Return the cooked beef into the skillet with the veggies. Mix them together.
Pour the sauce just prepared into the skillet with the veggies. Mix everything to coat the sauce evenly.
Cook for additional 2-3 minutes until everything is heated through and the sauce is thickened.
It’s time to serve the beef chop suey with the noodles or steamed rice.