Rinse tapioca (sabu dhana) really well. Soak in water overnight.
Boil and mash potato.
Dry roast peanuts over low heat and then cool. Crush using mortar & pestle until pieces are close to the size found in crunchy peanut butter.
Mix together tapioca, potatoes, peanuts, cilantro, chilis, ginger, chili powder, turmeric, cumin, salt, and fresh lemon juice.
Shape into ~1 inch round dumplings (vadas). Rubbing a little oil across both palms can help to prevent sticking.
Preheat oven to 375oF. Place a non-stick pan (taavi) on high heat. Place dumplings onto pan and cook for 1-2 minutes. Flip and cook for an additional 2 minutes. Dumplings will crisp up a bit through this process, yet they will not be fully cooked or crisp all the way around. Remove and allow dumplings to cool to touch.
Line a baking sheet with parchment paper. Place dumplings onto baking sheet, ensuring they do not touch each other. Bake at 375oF for 25 – 30 minutes or until golden brown.