Combine all of the ingredients for the BBQ sauce together in a medium saucepan. Bring to a boil and reduce heat to low and cook for 20 minutes, stirring occasionally until the sauce has reduced and thickened. Remove from heat and set aside.

Whisk together mayonnaise, vinegar, Dijon mustard, black pepper and salt together in a bowl. Mix in cabbage and toss to coat. Cover and refrigerate until ready to use.

Combine ground beef, onions, seasoning salt, pepper and 1/4 cup BBQ sauce together. Mix well. Divide into 4 equal parts. To form the burger patties roll each part into a ball and gently flatten. You want them to be larger than the hamburger buns at this point because they will shrink while cooking.

Heat grill to medium. Cook burgers 3 - 5 minutes on each side until cooked through. Brush burgers with remaining 1/4 cup BBQ sauce. Place cheddar cheese slices on top. Close grill lid and cook just until the cheese slightly melts, about 1 minute. Remove burgers from grill. Place on hamburger buns. Top with coleslaw. Serve.