Prepare the Aromatics: Set a large wok or a deep, heavy-based frying pan over a medium-high heat. Add the sesame oil and wait until it shimmers and you can smell its nutty aroma. Tumble in the diced onion. Cook for 3-4 minutes, stirring often, until it turns translucent and soft, and the kitchen begins to smell sweet and savoury.

Build the Fragrant Base: Add the minced garlic and grated ginger to the pan. Stir constantly for about 30 seconds, until the fragrance becomes incredibly potent and fills the air. You’ll hear a gentle sizzle—that’s the sound of flavour being born. Be careful not to let the garlic burn.

Brown the Chicken: Add the minced chicken to the pan, breaking it up with a wooden spoon. Cook for 5-7 minutes. You are looking for the chicken to lose its pinkness and take on a lovely, golden-brown colour. The sizzle will become more vigorous as the moisture evaporates, and the smell will shift to a rich, meaty savouriness.

Add the Crunch: Stir in the finely chopped water chestnuts and shiitake mushrooms. Cook for another 3-4 minutes. The water chestnuts will soften slightly but retain a wonderful, audible crunch. The mushrooms will release their moisture and then begin to brown, adding a deep, earthy layer to the aroma.

Create the Sauce: In a small bowl, whisk together the soy sauce, rice vinegar, hoisin sauce, and sriracha. Pour this mixture over the contents of the pan, stirring to coat everything evenly. Let it bubble and reduce for 1-2 minutes. The sauce will thicken and cling to the chicken, looking glossy and rich.

Finish and Serve: Remove the pan from the heat. Stir through the sesame seeds and half of the sliced spring onions. Taste and adjust the seasoning—perhaps a little more sriracha if you like heat. Arrange the lettuce cups on a large platter, spoon the warm filling into each one, and garnish with the remaining spring onions. Serve immediately, while the filling is hot and the lettuce is cool and crisp.