Grate the onion and add the grated onion and its juice to the Instant Pot. Add chicken, BBQ sauce, Worcestershire sauce, paprika and stock, then stir to combine.
Secure the lid and select Pressure Cook, setting the time for 5 minutes.
When the time is up, let the pressure naturally release for 10 minutes, then quick-release the remaining pressure and press cancel.
Remove the chicken and shred with 2 forks then return to the inner pot to combine with the juices and onion.
Select Saute and let the sauce come to a simmer for a few minutes to reduce any excess liquid.
Divide the chicken amongst the tortillas with shredded red cabbage and serve with lime wedges.