Preheat oven to 400 degree F. Line 2 baking sheets with parchment and lightly oil with oil spray. Set aside.
Peel onions. Slice onions ?" thick and separate slices into rings.
Mix together gluten free flour and baking powder. Whisk in water and oil. Depending on flour blend you used, you may need to add up to ? cup more water to create a batter the consistency of thick pancake batter. Pour batter into a shallow dish.
In another shallow dish, pour crush tortilla chips.
Using a fork or skewer, dip onion rings into batter, coating all sides. Tap off excess batter, as needed. Place onion ring into tortilla crumbs. Scoop crumbs over onion to coat all sides. Place coated onion ring onto prepared baking sheet. Continue with remaining onion.
Spritz onion rings with oil. Bake in preheated 400 oven until onion is tender and coating is cooked through and golden, 15 to 18 minutes.
Serve with your favorite dip. We especially like marinara sauce with this!