Place ¼ cup of the gluten-free flour on a plate. Set aside.
In a large bowl, whisk together the remaining flour, rice flour, sea salt, onion powder, garlic powder, white pepper, and sparkling water until the batter just begins to come together. The lightest tempura batter is achieved when the batter is barely mixed.
Heat at least 1” of oil in a large skillet over medium heat until it reaches 350° F.
BATTER AND FRY SQUASH:
Dredge each ring in the plate of gluten-free flour, shaking off any excess.
Working in batches so as to not overcrowd the skillet, dip a ring into the batter then immediately add it to the hot oil.
Fry until golden, about 2 minutes per side.
Remove and place on a wire rack to drain excess oil.
Repeat with the remaining squash.
FINISH AND SAERVE:
Sprinkle with a touch of flaky sea salt and serve immediately.