Heat the oil in a wok or pan. Fry the garlic in it over medium heat until golden brown. Add the meat and stir-fry for about 5 minutes, then mix in the onion. Season with fish sauce, sugar, salt and freshly ground pepper to taste and stir-fry for another 3 minutes.
Add bell pepper, cucumber, tomatoes, pineapple and spring onions, stir-fry for a few minutes.