In a small bowl, whisk together flour, 1/2 teaspoon onion powder, 1/4 teaspoon each salt and pepper. In another small bowl, whisk together the eggs and water. Place the panko in a third bowl. Dig the corn into the flour mixture, shaking off the excess. Dip in the egg mixture, shaking off the excess. Dig into the panko, making sure to completely cover the chicken.
Heat the oil in a large skillet over medium heat until shimmering. Working in batches of 2, cook the chicken, turning once, until golden brown and an instant-read thermometer inserted into the thickest side reads 165°F, 4 to 6 minutes in each group
Meanwhile, in a medium bowl, combine butter, mayonnaise, yogurt, herbs, remaining 1/2 teaspoon onion powder, 1/4 teaspoon each salt and pepper Add romaine and coleslaw mixture; Toss to coat. Top with the chicken and serve in a salad garnished with scallions, if desired.