Season chicken legs generously on all sides with barbecue seasoning.
Coat the inside of a slow cooker with cooking spray or insert a slow cooker liner.
Pour half of the barbecue sauce into the bottom of the slow cooker. Spread evenly.
Place the seasoned meat in the slow cooker in one layer.
Pour the remaining barbecue sauce over the meat, making sure each piece is coated evenly.
Cover and cook on low heat for 4-5 hours, high heat for 2 1/2-3 1/2 hours, or until the chicken is tender and cooked through.
Once the protein is cooked, carefully remove it from the slow cooker and transfer to an aluminum foil lined sheet pan. Turn the oven on broil.
While the oven heats up, carefully pour the remaining sauce from the slow cooker into a small skillet. On the stovetop, bring the mixture to a boil, then simmer for 5-10 minutes or until the liquid thickens and reduces by half.
Brush half of the thickened sauce over the cooked chicken legs.
Broil the legs for 2-3 minutes, or until the edges of the chicken skin are starting to brown.
Transfer the legs to a serving platter and serve the remaining barbecue sauce on the side.