Pat chicken pieces dry with paper towels. In a bowl, whisk together eggs and buttermilk until smooth. Submerge all chicken pieces in the buttermilk mixture, ensuring each piece is fully coated. Let sit in the refrigerator for at least 15-30 minutes.

In a large shallow bowl, combine flour, cornstarch, paprika, garlic powder, onion powder, salt, black pepper, and cayenne pepper. Whisk together well to distribute all seasonings evenly throughout the mixture.

Remove one piece of chicken from the buttermilk bath and let excess drip off. Roll it in the seasoned flour mixture, making sure it is completely covered on all sides. Press the coating gently onto the chicken. Place each coated piece on a clean plate or wire rack.

Heat oil in a deep pot or large skillet to 350°F using a thermometer. Working in batches to avoid overcrowding, carefully place coated chicken pieces into the hot oil. Fry for 12-15 minutes, turning halfway through, until coating is deep golden brown and internal temperature reaches 165°F.

Arrange fresh lettuce leaves on a large serving plate. Add crisp cucumber slices and halved cherry tomatoes around the plate. Scatter thin onion slices on top.

Pile fried chicken pieces onto the center of the plate over the fresh vegetables. Serve immediately while chicken is warm and crispy.