For the curry sauce: peel the onions and apples, cut into large pieces and boil in 50ml (a quarter of a cup) of water in a covered pot on low heat until soft and the water has evaporated.
Add the red curry paste, fish sauce, soy sauce, brown sugar, and coconut milk and blend until creamy.
Cut the beef into thin strips, slice the peppers and mushrooms, and then add to the pot with the sauce, along with the bamboo shoots. Let cook for 3-4 minutes after they start to boil.
Fry the tortillas. Add green coriander over the curry for extra flavor and decor.