In a bowl, whisk together the orange juice, brown sugar, BBQ sauce, chili powder, and red pepper flakes until the sugar dissolves and the mixture is uniform.
Place the chicken breasts in a gallon-size resealable bag and pour the marinade over them, pressing out excess air and sealing the bag.
Refrigerate the sealed bag for 2 to 4 hours to marinate, turning the bag occasionally to coat the chicken.
Preheat your grill or a cast-iron grill pan to medium-high heat and oil the grate or pan lightly.
Remove the chicken from the marinade and let excess drip off; discard the used marinade.
Grill the chicken 10 to 15 minutes, flipping once, until an instant-read thermometer inserted into the thickest part reads 165°F.
If desired, brush both sides of the chicken with additional BBQ sauce during the last minute of grilling, then remove from the heat and rest briefly before serving.