This recipe uses Open Nature cornbread mix; if using a different brand please adjust recipe ingredients and cooking times per package instructions.
Preheat oven to 375°F. Coat an 8-inch square baking dish with cooking spray. Prepare cornbread mix according to package instructions, using milk, melted butter, and egg. Bake until cooked through, then remove baking dish from the oven. Top cornbread with cheddar and jalapeño slices. Return to the oven and continue to bake until cheese is melted, 1-2 minutes more. Remove from oven and set aside to cool slightly.
While the cornbread is cooling, preheat an outdoor grill or grill pan over medium-high heat. Once hot, add chicken and grill until charred on one side, 4-6 minutes. Flip and cook an additional 5-10 minutes, until internal product temperature reaches 165°F on a meat thermometer. Remove from heat.
Meanwhile, place mayo, vinegar, Dijon, sugar, and spices in a medium bowl, then whisk to combine the dressing. Drain pickled onions and add to the bowl along with broccoli slaw. Stir to combine the slaw.
Thinly slice chicken. Cut cornbread into 2-inch squares, setting aside leftover cornbread for another meal.
Divide grilled chicken and slaw between plates. Serve with cheesy jalapeño cornbread on the side and enjoy!