Stir the palm sugar, lime juice, fish sauce, oyster sauce and soy sauce together in a small saucepan over medium-low heat until the sugar is completely dissolved; bring to a simmer. Set aside.
Heat the oil in a large frypan. Fry the garlic in the hot oil until browned; 7 to 10 minutes.
Add the onion; cook for 1 minute. Stir the cauliflower and carrot into the mixture; cook and stir for 1 minute.
Mix the cucumber, corn and peas into the mixture; cook for 1 more minute.
Stir the capsicum and tomato into the mixture; cook 1 minute. Pour the sauce over the mixture then add the pineapple and toss so the entire mixture is evenly coated in sauce; cook another minute. Serve hot