In a medium-sized bowl, add flour, salt, chili powder, garam masala, coriander, turmeric, and garlic. Stir to blend well. Make a well in the center of the mixture and gradually pour the water into it, blending as you go. Once a thick, smooth batter forms, add the cauliflower florets and onion rings. Gently stir until all surfaces are coated, adding 1 to 2 tablespoons of water if needed.

Pour the oil into a large, heavy skillet. Heat until an instant-read thermometer registers 375°F.

Fry in batches until golden brown, 3 to 5 minutes per batch. Transfer to a paper-towel-lined plate to drain. Serve immediately with your favorite dipping sauce.