Wash, peel, and cut potatoes into chunks. Chop or grate cauliflower and carrots. Rinse channa dal, boil with 2 cups water for 10 minutes. Add potatoes and salt, cook until tender, then mash with dal to form the base.

Add cauliflower, carrots, and peas to the mashed mixture, cook for 15 minutes until tender, adding water if needed. Meanwhile, heat oil in skillet, add mustard seeds and red chilies, then sauté onions until translucent.

Combine vegetable mixture with onions in skillet, cook for 5 minutes until saucy. Stir in red chili powder and pao bhaji masala. Toast bread rolls in skillet with oil until golden. Serve by placing vegetable filling on rolls and topping with tomato slices.