Make the chicken: Season the chicken with the chili powder and a generous pinch each of salt and black pepper. Set an Instant Pot to saute at high heat. When the display indicates ?hot,? add the olive oil. Working in batches, add the chicken and cook, turning, until browned, about 3 minutes; transfer to a plate. Add the red onion and garlic to the pot and cook, stirring and scraping up any browned bits from the bottom of the pot with a wooden spoon, until the onion is tender, about 5 minutes. Cancel the saute setting.
Return the chicken to the pot. Whisk the pineapple preserves, 2 tablespoons mustard, the cayenne and 1 cup water in a small bowl; pour over the chicken and stir to combine. Put on the lid, making sure the steam valve is in the sealing position, and set the cooker to high pressure for 6 minutes. When finished, carefully turn the steam valve to the venting position to release the pressure. Transfer the chicken to a plate and shred the meat into large chunks with 2 forks.
Set the cooker to saute at high heat. Bring the sauce to a simmer and cook until reduced by about half, about 8 minutes. Return the chicken to the pot and stir to coat. Continue to cook, stirring occasionally, until almost all the sauce is absorbed, about 10 minutes. Stir in the remaining 2 teaspoons mustard and the vinegar; season with salt and black pepper.
Meanwhile, make the slaw: Toss the coleslaw mix and bell pepper with 1/2 teaspoon salt and a few grinds of black pepper. Let stand 5 minutes. Add the coconut, scallion, cilantro, mayonnaise and vinegar and toss to coat. Season with salt and black pepper.
Divide the chicken among the buns and top with some of the slaw. Serve with vegetable chips.