Meanwhile, heat the olive oil in a nonstick skillet over medium high heat. Pan fry the chicken and onions just until the chicken is golden brown on each side. Set aside.
Put the peaches into the slow cooker and add the chicken, onions, BBQ, apple cider vinegar, and chipotle. Cook on high for three to four hours or low for six to seven hours.
Remove the lid and continue to cook the sauce on high. Remove the chicken and pull it into shreds. Return to the slow cooker to toss with the sauce. Adjust with salt and pepper, to taste.
Pile the chicken into the taco shells and top with cabbage, peaches, tomatoes, avocado feta, lime and cilantro, to taste.