Make the marinade by mixing together the sugar, salt, soy sauce and cornflour slurry. Mix in the beef, allow to marinate for 15 minutes.
Heat a large frying pan with 1 tablespoon oil. Stir fry the beef with 1/2 tablespoon garlic until 70% done, about 3-4 minutes. Set aside.
Heat the same frying pan with 1 tablespoon oil. Stir fry the remaining garlic until aromatic, 2-3 minutes. Add the onion and salt and stir fry until soft, 3 4 minutes. Add the capsicum; stir for 1-2 minutes.
Add the beef back into the pan together with the HP sauce and pineapple syrup. Mix to stir, adjust the seasoning with sugar, turn off the heat and add chopped pineapple, stir and serve.