Pound the chicken breasts slightly in their thickest part.
Mix the spices in a small bowl (sugar, chili powder, onion powder, garlic powder) and rub the chicken with the mix on all sides. Season with salt and pepper.
Heat the oil in a large frying pan over high heat. When hot, add the chicken, sear it on both sides until browned. It doesn't have to be cooked through at this point.
Add the bbq sauce, water, vinegar, and Worcestershire sauce. Turn the breasts to coat them in the sauce.
Cover the pan with a lid and cook the chicken over low heat for 5-10 minutes or until cooked through. You can check if the chicken is done by measuring its temperature in the thickest part of the breast with an instant-read thermometer - it should be 165°F (74°C). You can also just cut the meat in its thickest part to check its color - it should be white and not pink.
When the chicken is ready, take the pan off the heat and shred the meat using two forks into bite-sized pieces. Toss the pulled chicken with the sauce until evenly coated.