Grind ginger root and chillies in a food processor. Add mint, tofu, and water as needed. Blend until smooth creamy paste is formed. Add this mixture to the dosa batter. Mix cumin seed and salt in the batter. Add additional water as needed to make batter similar to thick cream. Heat a skillet and wet It with 10 ml of oil. Put about 80 ml of batter in the skillet, wait for few seconds, and gently spread the batter uniformly over a about 15 cm (6″) diameter circle. Cook for about 2 minutes on one side and then flip and cook about 1 minute on the other side. Flip and cook until light brown on both sides. Serve hot with chutney and sambar .