Shred the carrot using a julienne peeler or cut into thin matchsticks. Halve the cucumber lengthwise, then put, cut-side down, on a board. Lightly smack with the flat side of a large knife or a rolling pin, then coarsely chop. Thinly slice the spring onion on an angle, keeping the white and green parts separate. Coarsely chop the peanuts.
Step 2 — Pickle carrot
Combine 2 tsp white vinegar and 1 tsp sugar in a bowl. Add the carrot and toss to coat. Set aside to pickle, tossing occasionally, until needed.
Step 3 — Make cucumber salad
Combine 2 tsp white vinegar, 2 tsp soy sauce and ½ tsp sugar in a bowl. Add the cucumber and white part of the spring onion and toss to coat.
Step 4 — Cook mushroom meat
Heat 2 tsp oil in a medium frypan over high heat. Cook the mushroom meat, breaking up the lumps with a spoon, for 2-3 mins until starting to brown. Add the Chinese barbecue seasoning, kecap manis and 1½ tbs water and cook, stirring, for 1 min or until fragrant and browned.
Step 5 — Warm bao buns
While the mushroom meat is cooking, remove the bao buns from the bag and put on a plate. Cover with a microwave-safe bowl and microwave for 2 mins or until fluffy and heated through. (Alternatively, follow the steaming instructions on the packet.)
Step 6 — Get ready to serve
Drain the carrot, discarding the pickling liquid. Divide the bao buns among plates, then fill with the carrot, mushroom meat, peanuts and remaining spring onion. Serve with the cucumber salad.