Finely chop onions, green chilies, and coriander leaves together.
Heat a flat griddle and ladle a thick circle of dosa batter without spreading too thin.
Sprinkle the chopped onion and chili mixture generously over the top, pressing gently into the batter.
Drizzle sesame oil around edges, cover with a lid to cook through, flip, and brown the other side before serving hot.