Pat dry the chicken thighs with a kitchen towel.
Place the chicken thighs, chili powder, paprika, onion powder, garlic powder, salt, pepper, grated onion, BBQ sauce, brown sugar, Worcestershire sauce, and chicken stock in the Instant pot. Close the Instant Pot with lid and make sure the valve is in the sealing position.
Press the “Manual” setting and cook the chicken for 12 minutes. Once the cycle is done, allow the pressure to release naturally for 10 minutes and release the remaining pressure.
Carefully open the lid, remove the chicken, and shred it with the help of a fork. Transfer the chicken back to the instant pot and simmer for a couple of minutes until everything comes together.
Meanwhile, prepare the coleslaw by combining the coleslaw ingredients in a wide bowl. Mix it well.
Place the shredded BBQ chicken in a Hamburger bun and top it with coleslaw to serve.