How to Make It
Place eggplant in a colander. Toss with 1 teaspoon salt and let sit for 15 minutes; rinse and squeeze gently to remove excess water.
Meanwhile, in a small bowl, stir together ponzu, lime juice, ginger and scallion. Set aside dipping sauce.
In a Dutch oven, heat 1 1/2-inches of oil to 365°-370°. In a large bowl, whisk together flour, cornstarch, baking powder and 1 teaspoon salt. Gently whisk in club soda just until batter comes together (do not overmix, some lumps are OK). Working in batches, dip squash, potato and lemon into batter, letting excess drip off, and place into hot oil. Fry, turning occasionally, until cooked through, light golden and crispy, about 2 minutes (wait for oil to return to 365°-370° between batches). Transfer to a paper towel–lined wire rack set over a baking sheet to drain. Repeat with kale leaves, if using (be careful, oil will splatter), frying a few leaves at a time. Season tempura with salt and serve with dipping sauce.