Mix together the semolina flour and yogurt to form a batter. It should have the consistency of pancake batter; add a couple of tablespoons of water if necessary to make the batter easily spreadable. Mix in the salt and the oil. Allow to rest for 20 minutes on the counter.
Heat a little bit of oil in a non-stick skillet. Pour a ladle of batter and spread a bit. Add the chopped onions, tomatoes and coriander.
Let it cook for a couple of minutes on one side and then flip. Cook for another couple of minutes, till the batter is set (cook as you would a pancake, although it takes a few minutes longer since it is thicker and denser).
Remove to a plate and repeat with the remaining batter. Sprinkle with cilantro garnish and serve.
Notes
Kosher dairy, vegetarian
Recipe by Katherine Martinelli at http://www.katherinemartinelli.com/blog/2011/secret-recipe-club-rava-uttapam/