Slice the onions into very thin slices, then dice the cilantro and the chile (discard the seeds).
In a large bowl, combine the chickpea flour, baking powder, 1 teaspoon salt, 1 teaspoon cumin, and turmeric. Then add the diced chile, 2 tablespoons of cilantro, lemon juice, and water.
Stir well, then add the onions. Mix with your hands to coat the onions in the batter. Form the onion mixture into 8-10 patties. They will be irregular in shape and this is fine.
Pour the oil into a large skillet and bring the heat to medium-high. When the oil is hot, put as many patties as possible that will fit into the skillet. Cook for 3-4 minutes on each side until they are golden brown. Remove them from the pan and set them on a surface lined with paper towels to dry.
Prepare the raita by adding the yogurt, cucumber, garam masala, and the remaining cilantro, cumin, and teaspoon of salt. Blend until smooth.