Thinly slice onion and soak in buttermilk for 20 minutes. Combine flour and 1 tablespoon Cajun Seasoning; set aside.
Meanwhile, prepare burgers. Season ground turkey with remaining 1 tablespoon Cajun Seasoning. Shape into 4 patties.
Preheat grill or grill pan over medium heat. Clean and grease the grill grates. Cook burgers for about 5-7 minutes on each side or until cooked through: 165°F.
Meanwhile, heat Natural Grapeseed Oil in a small saucepan over medium heat until shimmering. Working in batches, remove onions from buttermilk, shaking off any excess, then coat in flour. Fry onions for about 2 minutes or until golden and crispy. Drain on a paper towel-lined plate.
Assemble burgers on buns with lettuce, tomato, and fried onions.
