How to Make It
Process onion, soy sauce, sesame oil, garlic, lemon zest and juice, and 2 teaspoons salt in a blender until smooth.
Place chicken in a baking dish or large ziplock bag and pour marinade over chicken. Turn to coat the chicken; cover or seal, and chill for at least 4 hours.
Remove chicken from marinade; discard marinade. Place chicken and cornstarch in a large bowl. Toss to coat. Shake off excess; arrange chicken on a wire rack set in a baking sheet. Let chicken stand at room temperature until dry and cornstarch no longer appears powdery, about 1 hour.
Heat 2 inches of canola oil in a large high-sided skillet or pot to 350°F. Working in batches, fry chicken until light golden and cooked through, 3 to 4 minutes, turning occasionally with a mesh skimmer or large slotted spoon. Using a mesh skimmer, transfer chicken to a clean wire rack and season lightly with salt.
In the same oil, fry the rice cakes in batches until crispy, 20 to 25 seconds. Season the rice cakes with salt. Serve chicken and rice cakes with gochujang.