Kitchen Tip: To sear lemon slices, heat 2 teaspoons oil in a skillet over medium-high heat. Add lemon slices; cook, turning frequently, until browned, about 2 minutes.
Preheat oven to 350°.
In a 12-inch cast-iron skillet, heat oil over medium-high heat. When oil is hot, reduce heat to medium. Sprinkle chicken with 2 teaspoons salt and 1/2 teaspoon black pepper. Working in batches, add chicken to skillet; cook, turning occasionally, until browned, about 6 minutes. Remove from skillet.
Add onion to skillet; cook, stirring occasionally, until lightly browned, about 5 minutes. Add rice, garlic and red pepper; cook for 2 minutes. Add broth, lemon juice, remaining 1/2 teaspoon salt and remaining 1/2 teaspoon black pepper; bring to a boil over medium-high heat. Remove from heat; arrange chicken in rice mixture.
Bake, covered, until rice is tender and a thermometer inserted in thickest portion of chicken registers 165°, about 35 minutes. Let stand, covered, for 10 minutes. Sprinkle with parsley. Garnish with seared lemon slices, if desired.