Combine the onions and buttermilk and refrigerate for 8-12 hours.
Pre-heat the oven to 250°F.
Heat a few inches of oil to 350°F or set up a tabletop fryer. Combine the flour and cornmeal and toss in the O-rings to coat. Add to the hot oil and fry for 3 minutes, to golden. Season with salt and drain on paper towels. Keep warm in the oven on a wire rack set onto a baking sheet.
Combine the meat and spices, grated onion, garlic, Worcestershire, mustard, salt and pepper. Form four patties, thinner at the center and thicker at the edges for even cooking.
Heat a cast iron skillet over medium-high heat. Combine the ketchup and Sriracha sauce in a small bowl.
Brush the pretzel buns with a little water and sprinkle with the salt included in the package. Warm the pretzel buns in the oven for 5 minutes and split them open.
Cook the burgers in the hot skillet for 8 minutes, turning once.
Serve the burgers on a bed of shredded lettuce topped with 2-3 crispy rings and some spicy ketchup.