Pat the chicken thighs dry and season with salt, garlic powder, onion powder, and plenty of freshly ground black pepper. Heat the olive oil in a large skillet over medium-high heat. Add the chicken and cook for 3 to 4 minutes per side, until golden brown. Transfer the chicken to a plate, leaving the juices in the pan.
Reduce the heat to medium-low and add the garlic and onion. Cook for 5 minutes, stirring occasionally, until the onions are very soft. Stir in the broth, rice, dill, and salt, making sure to scrape the bottom of the pan to incorporate the seasoning from the chicken. Bring to a boil, then reduce to a simmer and place the browned chicken thighs on top. Cover with a lid and cook over low heat for 15 to 18 minutes, until the rice is tender and the liquid has been absorbed.
Meanwhile, in a medium bowl, mix together the ingredients for the gremolata.
Remove the pan from the heat and let it sit, covered, for 5 minutes. Uncover, fluff the rice with a fork, and sprinkle with the gremolata before serving warm.
