How to Make It
Preheat the oven to 300°. Sprinkle the eggplant slices with salt and let stand on a rack set over a rimmed baking sheet for 20 minutes. Rinse and pat dry.
Meanwhile, using a sharp knife, slit the squid bodies lengthwise and lay them flat on a work surface with the insides facing up. Using the tip of the knife, score the bodies in 1/8-inch-diagonal diamonds, being sure not to cut all of the way through. Cut the squid in quarters lengthwise.
In a medium bowl, whisk the egg whites with the cornstarch. Put the panko in a shallow bowl and season lightly with salt. Dip the eggplant rounds in the cornstarch mixture, spreading it thinly with your fingers. Dredge the eggplant in the panko, pressing to help the crumbs adhere. Transfer the eggplant to a baking sheet.
In a large skillet, heat 1/4 inch of canola oil until shimmering. Add half of the eggplant and fry over moderately high heat, turning once, until golden and crisp, about 5 minutes. Drain the eggplant on paper towels and sprinkle lightly with salt. Repeat with the remaining eggplant. Transfer the eggplant to a wire rack and keep warm in the oven. Pour out the oil and wipe out the skillet.
Add 3 tablespoons of oil to the skillet and heat until smoking. Add half of the squid and stir-fry over high heat until curled and lightly browned, about 4 minutes. Pour the squid and any accumulated liquid into a bowl. Add 3 more tablespoons of oil to the skillet; when it shimmers, add the remaining squid and stir-fry. Return all of the squid and any accumulated liquid to the skillet and cook over high heat until the liquid is evaporated, about 2 minutes. Add the scallions, season with salt and cayenne and cook until the scallions are tender, about 1 minute. Transfer the squid and eggplant to plates. Sprinkle with the cashews and serve with lemon wedges.