First thing, need to clean the heart, cut in half lengthwise, remove the string parts and cut off the tubes on the top end and discard those. Wash the heart and remove any blood. Slice the heart lengthwise into strips. Add the pieces to a bowl and add salt and pepper as desired, mix well and let sit for 15 minutes.
For the cucumber, cut in half lengthwise scoop out seeds, then cut each piece into thin slices. Prep the rest of the vegetables and fruit as stated.
Heat a non stick pan with a splash of cooking oil, when heated, add the ½ the onion and stir fry until soft, then add the heart and stir fry until the heart is cooked through, remove the heart and onion and set aside.
Same pan, add the remaining onion and stir fry for 2 minutes. Add the tomato, pineapple, cucumber and stir fry. Add the fish sauce, Maggi sauce, and salt as desired. Continue to stir fry to soften the cucumber and tomato.
Add the heart back to the pan, mix, adjust seasoning to taste with fish sauce or salt, and pepper. When the heart is warmed through, remove from heat.
Garnish with chopped spring onion, serve with rice.