Barbecued Sweet Potatoes

Barbecued Sweet Potatoes
Weight Watchers 1.5 points

2 tablespoon ketchup plus 2 teaspoons
1 tablespoon Worcestershire sauce
1 tablespoon red wine vinegar
1 teaspoon yellow mustard
1/2 teaspoon freshly ground black pepper to taste
1 pound sweet potatoes pared cut into 1/4" slices

Prepare grill for a medium fire.