Nick,mix tomato sauce, chile sauce, rice vinegar, sugar, water, cornstarch for sauce.
Marinade pork shoulder cubes in a mixture of egg yolk, sesame oil, salt, 5 spice powder and wine (chinese).
Then coat with cornstarch and fry in wok until crispy, drain.
Fry onion in wok,cook then add tomatoes. Add sauce, cook together the pour over pork, mix.