Using paper towel, pat dry the chicken, place in a big bowl and season with a pinch of salt and pepper. Then marinate the chicken in pineapple juice from the can of pineapple chunks for about 30 minutes to 1 house. Stir for a couple of times until all chicken are well coated with pineapple juice. Cover and let it rest inside the refrigerator.
After marinating, using a wok or large deep skillet, heat the oil over medium high heat. Then saute the onions, garlic and tomatoes until the aromatic start to spread.
Remove the chicken from the pineapple juice mixture using tongs, save the marinade. Stir fry the chicken for a 2 minutes then add the potatoes and carrots in the pan. Season with a pinch of salt and pepper. Stir continuously for additional 3 minutes.
Pour the water or chicken broth, marinade sauce (pineapple juice) and coconut milk, stir the mixture and season with fish sauce and red pepper flakes. Cover and bring them to boil. Simmer over medium heat, stirring occasionally until the chicken and potatoes are cooked through.
Uncover, then add the bell peppers and pineapple chunks into the mixture. Stir and adjust the seasonings if needed. Lower the heat and let it simmer until the bell peppers are crisp and tender.
Turn off the heat, transfer the dish to a serving dish ad serve with steamed white rice and enjoy!