Check your avocado is ripe before starting this recipe (see cooking tip). Cut the cucumber into short batons. Combine the mirin and 2 tsp white vinegar in a large bowl. Add the cucumber and toss to coat. Set aside to pickle, tossing occasionally, until needed.
Step 2 — Prep aioli and togarashi
Put the aioli in a bowl and swirl through the sriracha sauce. Combine the sesame seeds and shichimi togarashi in a separate bowl.
Step 3 — Prep fillings
Thinly slice the avocado. Thinly slice the pak choy. Put the pak choy in a bowl, drizzle with the sesame oil and toss to combine.
Step 4 — Cook prawns
Heat 2 tsp oil in a medium frypan over high heat. Cook the prawns, stirring, for 2-3 mins until just cooked through. Add the sweet chilli sauce and cook for a further 1 min or until the prawns are well coated. Season with salt and pepper.
Step 5 — Heat bao buns
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
Spread the bao buns with the sriracha aioli, then fill with the prawns, seaweed, avocado, pickled cucumber and pak choy. Scatter over the sesame togarashi. Add the remaining avocado and pak choy to the pickled cucumber in the bowl and toss to combine. Scatter with the remaining sesame togarashi and serve with the prawn bao buns.