Cut all vegetables and meat into bite-sized pieces.

Heat oil in a pan and cook the meat until lightly browned.

Add onion and carrot; stir-fry briefly.

Add bell pepper, cucumber, pineapple, and tomato.

Mix oyster sauce, tomato sauce, soy sauce, and sugar to form the sweet and sour sauce.

Pour sauce into the pan and stir until evenly coated.

Simmer briefly until vegetables are just tender.

Taste and adjust sweet and sour balance.

Garnish with spring onion and serve.