How to Make It
Gather all ingredients, and preheat the oven to 350 degrees F (180 degrees C).
Sprinkle chicken on both sides with salt and pepper.
Heat 2 tablespoons olive oil in a 5- to 6-quart Dutch oven over medium-high heat. Add half the chicken thighs. Cook until seared and lightly browned, 4 to 5 minutes each side. Transfer browned chicken to a plate. Repeat with remaining chicken.
Reduce heat to medium. Add remaining 1 tablespoon olive oil to Dutch oven. Add onions. Cook until tender and lightly browned, stirring occasionally, 3 to 4 minutes. Stir in minced garlic, cooking until fragrant, about 30 seconds.
Add butter to Dutch oven. Once melted, add orzo, quickly stirring until fully coated with butter. Carefully pour in chicken broth. Scrape bottom of Dutch oven with a wooden spoon to loosen any browned bits. Bring to a boil, then remove from heat.
Bake, covered, in the preheated oven until orzo has absorbed most of the liquid, about 15 minutes.
Remove Dutch oven from oven. Stir in spinach, Parmesan, dried tomatoes, lemon zest, and lemon juice.
Nestle chicken thighs into orzo mixture. Cover, return to the oven, and bake until chicken is no longer pink at the center and an instant-read thermometer inserted near the center reads at least 165 degrees F (74 degrees C), 10 to 15 minutes. Serve immediately with lemon wedges.