Preheat the oven to 450°F. Coat a baking sheet lightly with cooking spray and set aside. Place the potato chips in a food processor and process into fine crumbs, about 20 seconds. Transfer to a shallow bowl, stir in the cayenne, and set aside. In another bowl, combine the buttermilk, 2 Tbs. of the flour, the salt, and pepper and set aside.
Slice the onions into 1/2 -inch-thick rounds and separate into rings, keeping only the large, whole rings (reserve the rest of the onion for other uses). You should have 12 to 14 rings.
Place the remaining 1/2 cup flour in a sealable plastic bag, then add the onions and shake to coat. One at a time, dip the onion rings into the buttermilk mixture, then dip into the potato chip crumbs, coating each ring evenly, and place on the baking sheet. Coat the surface of the rings lightly with canola oil spray and bake until the coating is crisp, about 20 minutes. Season with salt and serve immediately.