Preheat a grill to 400 degrees F using indirect heat. Oil the grill grates.
Cut the potatoes into 1-inch chunks and add to a bowl with the olive oil, garlic salt and pepper. Toss to coat. Place the potatoes directly on the oiled cooking grates (if needed, use a grill basket so the potatoes don't fall through). Cook, turning as needed, until done, about 30 minutes.
In a mixing bowl combine the mayonnaise, KC-Style Chipotle BBQ Sauce and jalapeno juice. Gently fold in the warm potatoes, bacon, celery and green onions. Garnish with a couple slices of green onion on top and serve immediately.
Mix together the ketchup, sugar, chipotle, Worcestershire, molasses, vinegar, ancho powder, salt, pepper, cocoa, liquid smoke, oregano, thyme and mustard powder in a saucepan and gently warm over medium heat, stirring continuously, until the sugar dissolves. Do not boil.
The sauce can be used immediately. The flavors will continue to meld if allowed to rest in the refrigerator overnight.
You can substitute white vinegar for the pickled jalapeno juice. To cook the potatoes in the oven, preheat the oven to 400 degrees F with a sheet pan inside. Spray the pan with cooking spray and place the potatoes on the hot sheet pan. Cook, turning halfway, until done, about 30 minutes.