Beat together the egg, milk, chickpea flour, all-purpose flour, baking powder, turmeric, chili powder, cumin, coriander and salt in a large bowl.
Stir in the sliced onions.
Heat the oil to a large skillet or cast iron pan to 350 degrees.
Working in batches, drop spoonfuls of batter into the oil, being careful not to crowd the pan. Fry for 2 to 3 minutes on each side or until golden brown. Remove with a slotted spoon to a paper towel lined plate. Repeat until you’ve fried all the batter.
Stir together the cucumber sauce ingredients and serve with the onion fritters.