In a small bowl, combine garlic powder with onion powder, 1/4 teaspoon Kosher salt, and 1/4 teaspoon ground black pepper.
Lay the thighs atop a sheet of parchment paper to prevent contaminating kitchen surfaces and brush both sides with 1 tablespoon of olive oil between all of them.
Sprinkle both sides of all of the chicken pieces with the dry mixture and allow to come to room temperature.
Use a sharp knife to cut the root tip from the radishes as well as the greens if they are present.
Add the prepared radishes and red onions to a small bowl and toss with the remaining tablespoon of olive oil and some additional Kosher salt and black pepper.