Wash and dry all produce. Halve and core apple; dice one half into bite-size pieces and other into slices (dice whole apple for 4 servings). Zest and quarter lime. Trim and thinly slice scallions, separating whites from greens.

Squeeze juice from half the lime into a large bowl. Stir in sour cream, 1/2 tsp sugar (1 tsp for 4 servings), and lime zest to taste. Add diced apple and half the cabbage (you’ll use the rest later); toss to combine. Season with salt and pepper.

Pat chicken dry with paper towels; season all over with salt and pepper. Heat a large drizzle of oil in a large pan over medium-high heat. Add chicken, scallion whites, and remaining cabbage. Cook, stirring occasionally, until chicken is cooked through, 4-6 minutes.

Add BBQ sauce to pan; stir until everything is coated. Turn off heat and stir in 1 TBSP butter (2 TBSP for 4 servings) until melted.

Wrap tortillas in damp paper towels and microwave until warm and pliable, 30 seconds.

Divide chicken mixture between tortillas. Top with slaw and scallion greens. Serve with sliced apple, if you have any, and remaining lime wedges on the side.