To make the bhaji (vegetable), heat butter in a pan and add cumin seeds. Once they splutter, add chopped onions, ginger, garlic, and green chilies. Cook until the onions turn translucent.
Add the chopped vegetables, salt, and all the spices. Mix well and cook until the vegetables are soft and fully cooked.
Mash the cooked vegetables with a potato masher or the back of a ladle. Add water if needed to adjust the consistency.
Heat a dosa tawa or griddle on medium heat. Once hot, spread a ladleful of dosa batter on the tawa and spread it evenly in a circular motion.
Drizzle oil around the edges and cook until the bottom turns golden brown.
Serve the dosa with generous portion of the prepared bhaji.