In a microwave safe bowl, rinse the tapioca pearls 3 to 4 times till the water you're rinsing with becomes almost clear. Drain and add 1/4 cup of water to the bowl and let tapioca pearls soak for 3-4 hours.
Tapioca is done soaking when, if squeezed between two fingers, it will feel spongy with no hardness left. All the tapioca should also be separated. Drain any excess water from the bowl that is left.
Add walnut powder, salt and coconut sugar to the tapioca pearls and mix well.
Heat a small frying pan on medium heat and add ghee. Once ghee is melted and hot, add cumin seeds and let them roast in the oil for 30-60 seconds.
Then, add the serrano chilies and boiled, cubed potatoes. Saute for a couple of minutes and then add all of this to the tapioca-walnut mix in the bowl.
Microwave all of this for 2 minutes. Make sure the bowl is not covered when microwaving. When finished, remove and stir. Now, add lemon juice, and again microwave for one minute uncovered.
Remove from microwave and stir. Taste and adjust salt, sugar and lemon juice to taste.
Microwave one last time for 30-45 seconds. Remove, stir and garnish with chopped cilantro.