Pat the chicken dry and pound to an even thickness if needed, then season both sides with salt, pepper, garlic powder, and 1 tsp dried parsley.
Heat a large skillet over medium-high heat and add the olive oil and butter until melted and shimmering.
Sear the chicken in the hot skillet until browned on both sides but not cooked through, about 2 minutes per side; transfer the chicken to a plate.
Reduce heat to medium, add the uncooked rice to the skillet and stir to coat with the pan fat, scraping up any browned bits.
Pour in 2 1/4 cups chicken stock, add the lemon zest, 3 tablespoons lemon juice, and the remaining 1 tsp dried parsley (or fresh parsley), and bring to a gentle boil.
Lower the heat to a simmer, nestle the seared chicken on top of the rice, cover with a lid, and cook for 20–22 minutes until the rice is tender and liquid is absorbed and the chicken is cooked through.
Remove the lid, fluff the rice with a fork, and garnish the chicken with lemon slices and extra parsley if desired before serving.