Crush or finely chop the garlic. Cut the onion into thin wedges. Coarsely chop the capsicum. Cut the leaves from the pak choy, quarter the stems lengthwise, then thickly slice.
Step 2 — Prep beef
BEEF STIR-FRY OPTION Combine the garlic, Chinese barbecue seasoning and 2 tsp oil in a large bowl. Separate the beef stir-fry, add to the seasoning mixture and stir to coat.
Step 3 — Cook beef
Heat 2 tsp oil in a large deep frypan over high heat until very hot (beef stir-fry is best with hot, fast cooking; get the pan very hot before adding the beef and stick to the short cooking time). Stir-fry the beef for 1-2 mins until browned. Remove from the pan.
Step 4 — Start stir-fry
Heat 2 tsp oil in the frypan over medium-high heat. Cook the onion and capsicum, stirring regularly, for 3-4 mins until starting to soften.
Step 5 — Prep and add sauce
Meanwhile, combine 1½ tbs sweet chilli sauce*, 1 tbs oyster sauce* and 2 tsp soy sauce in a bowl. Add the pak choy stems and sauce mixture to the onion and capsicum. Increase the heat to high and cook, stirring, for a further 1-2 mins until the pak choy is just tender.
Step 6 — Finish stir-fry and serve
Add the beef and pak choy leaves to the vegetables and cook, stirring, for 1 min or until the leaves are wilted. Divide the beef stir-fry among bowls and scatter with the sesame seeds to serve.