Sift chickpea flour into a medium bowl; mix in garlic, salt, coriander, turmeric, chili powder, and garam masala. Make a well in the center; gradually pour water into the well and mix to form a thick, smooth batter.

Heat oil in a large heavy saucepan over medium-high heat to 375 degrees F (190 degrees C).

While the oil is heating, dip cauliflower florets and onion rings in batter to coat.

Working in small batches, fry battered vegetables in hot oil until golden brown, about 4 to 5 minutes. Drain on paper towels before serving.