Place the chicken breasts and water in the Instant Pot. Select “Pressure Cook” or “Manual” on high and set the timer to 8 minutes. Let the Instant Pot naturally release for 5 minutes before performing a manual release.
While the chicken cooks, combine the cabbage, carrot, bell pepper, mayonnaise, vinegar, salt and pepper to make the slaw. Set aside until you’re ready to assemble the cups.
Drain the water and any excess liquid from the chicken and shred.
Mix the BBQ sauce into the shredded chicken.
When you’re ready to serve, spoon chicken into a piece or two of butter lettuce and top with slaw.