In a large bowl, mix buttermilk and adobo sauce until combined. Soak onion rings in adobo buttermilk in refrigerator for 2 hours.
Preheat oven to 450. Prepare a large baking sheet with parchment paper.
Mix together the Panko, bread crumbs, salt and pepper. Set half of the breading mixture aside.
Using tongs, dip soaked onions into breading mixture, thoroughly coating on both sides. Place onions onto parchment paper. When breading is used up (or too wet to stick to onions), switch to the other half of breading mixture. Repeat until all the onion rings are coated. Spray entire pan of rings generously with cooking spray.
Bake in 450 oven until brown and crispy, 12-15 minutes.
Season with coarse sea salt. Serve.