Preheat the grill to high heat, about 400˚F.
Make the sauce by combining all of the ingredients for the dip in a small bowl, whisking until smooth. Season to taste with salt.
To prep the onions, start by cutting off the stem. Turn the onion cut side down. Cut ½-inch from the root down, cutting the onion into about 10 to 16 sections. Be sure not to cut through the root. Flip over and gently separate the petals. Sprinkle all over with Head Country BBQ Original Championship Seasoning.
Add the onions to the hot grill, cooking until tender and lightly charred, about 15 minutes. After 10 minutes of grilling, brush with BBQ sauce all over. Make sure you apply a generous layer of sauce! Grill for the remaining 5 minutes to set the glaze.
Garnish with freshly chopped parsley and serve with dipping sauce.