Wash and dry the water spinach and use your hands to break the stems into 2" pieces.
Heat oil on high heat until the pan is very hot. Add garlic and bean sauce and saute for ~10 seconds until the garlic turns golden brown, being careful not to burn it!
Quickly add the water spinach, peppers, and oyster sauce. Use two spatulas to stir fry until the water spinach starts to turn bright green (should be less than a minute).