Step 1

For the pickled onion: Bring the vinegar, sugar, salt, red pepper flakes and 1/2 cup water to a boil in a small saucepan. Put the red onion in a heatproof bowl and pour the vinegar mixture on top. Cover and refrigerate until ready to serve.

Step 2

For the pork: Whisk 2 tablespoons brown sugar, the ginger, five-spice powder, salt, pepper and mustard powder in a large bowl. Add the pork, turning to coat in the rub. Add the olive oil to a 6- or 8-quart Instant Pot and set to sauté. When hot, add the pork and brown 2 minutes per side. Remove to a plate. Add the broth to the pot and scrape up the browned bits from the bottom. Whisk in the hoisin sauce, soy sauce, vinegar, chili sauce and Sriracha. Return the pork to the pot.

Step 3

Put on and lock the lid, making sure the steam valve is in the sealing position. Set to pressure-cook on high for 45 minutes. After the time is up, let the pressure release naturally for 10 minutes, then carefully turn the valve to the venting position to release the remaining pressure. Turn off the pot and remove the lid. Remove the pork to a baking sheet and shred with 2 forks.

Step 4

Set the Instant Pot to sauté, then stir in the remaining 1/2 cup brown sugar. Remove 3 tablespoons of the liquid from the pot to a small bowl; whisk in the cornstarch. Pour the cornstarch mixture into the pot and cook, stirring, until the sauce is thickened, about 10 minutes; season with salt. Return the pork to the pot and stir. Serve the pork in the lettuce leaves and top with the pickled onion, sesame seeds and scallions.