Combine soy sauce, lime juice, green onion, sliced onion, chopped jalapeno, and sugar in a small bowl; stir thoroughly until the sugar has dissolved, then set aside.
Place the grated potato and onion into a mixing bowl, sprinkle in the salt, and incorporate the potato starch by stirring until the mixture is uniform.
Preheat a 9 to 12-inch nonstick skillet over medium-high heat, then pour in 2 tablespoons of the grape seed oil, swirling to coat the base evenly. Spread the potato mixture evenly and thinly across the pan.
Cook for several minutes until the underside becomes crisp and takes on a light golden hue.
Flip the pancake carefully with a spatula, pour the remaining oil around its edges, and tilt the pan to allow the oil to flow underneath. Continue cooking until the other side is equally golden and crisp.
Repeat flipping as needed until both sides achieve a uniform crispness, typically after 8 to 10 minutes total cooking time.
Slide the pancake onto a serving plate and offer it hot with the prepared dipping sauce.