First make shredded chicken*. Place sliced onions in a single layer on the bottom of a slow cooker, cover with chicken and season well with salt and pepper. Pour 1/2 jar of Stubb's Smokey Mesquite Bar-B-Q sauce over the chicken, cover and cook on low 6-8 hours.
In a small bowl combine 1/2 cup sour cream and 1/2 cup Stubb's Smokey Mesquite Bar-B-Q sauce (make more or less depending on how many you are serving). Keep refrigerated until ready to serve.
When chicken is done, remove it from the slow cooker using a slotted spoon and shred in a bowl using two forks. Add a few tablespoons of leftover cooking liquid to the chicken, along with more Bar-B-Q sauce, until it is coated evenly.
Preheat oven to 425°F and set out a piece of parchment paper for assembling.
Lay egg roll wrappers flat on parchment paper and top with a spoonful of shredded carrots, one slice of avocado and a spoonful of shredded chicken. Moisten the edges of the egg roll wrapper, fold two opposite edges toward the center and then fold in the remaining two edges, rolling so that the seam is on the bottom.
Bake egg rolls on a parchment lined cookie sheet until lightly browned & crispy (15-20 minutes).
Serve with creamy Bar-B-Q dipping sauce.