In a large bowl, combine ground chicken, panko breadcrumbs, feta cheese, egg, red onion, garlic, parsley, oregano, salt, and pepper. Mix until just combined.
1 pound ground chicken, 0.25 cup panko breadcrumbs, 0.25 cup crumbled feta cheese, 1 egg, 0.25 cup finely chopped red onion, 2 cloves garlic, 2 tablespoons chopped fresh parsley, 1 teaspoon dried oregano, 0.5 teaspoon kosher salt, 0.25 teaspoon black pepper