Collect all the necessary ingredients and preheat the oven to 350°F (180°C), ensuring everything is ready for cooking.
Season the chicken on both sides with salt and pepper, ensuring an even coating for flavor.
In a 5- to 6-quart Dutch oven, heat 2 tablespoons of olive oil over medium-high heat. Add half of the chicken thighs and cook until they are seared and golden brown, about 4 to 5 minutes per side. Once browned, transfer the chicken to a plate. Repeat the process with the remaining chicken thighs.
Lower the heat to medium and add the remaining 1 tablespoon of olive oil to the Dutch oven. Toss in the onions and cook, stirring occasionally, until they are soft and lightly browned, about 3 to 4 minutes. Add the minced garlic and cook for an additional 30 seconds, or until fragrant.
Add the butter to the Dutch oven and let it melt. Once melted, stir in the orzo, making sure each grain is well coated with butter. Gradually pour in the chicken broth, using a wooden spoon to scrape up any browned bits from the bottom of the pot. Bring the mixture to a boil, then remove the Dutch oven from the heat.
Cover the Dutch oven and bake in the preheated oven for about 15 minutes, or until the orzo has absorbed most of the liquid.
Take the Dutch oven out of the oven and stir in the spinach, Parmesan, sun-dried tomatoes, lemon zest, and lemon juice, blending everything together until well combined.
Place the chicken thighs back into the orzo mixture, ensuring they are nestled in. Cover the Dutch oven and return it to the oven. Bake for 10 to 15 minutes, or until the chicken is fully cooked, with no pink in the center, and an instant-read thermometer registers 165°F (74°C). Serve immediately, garnished with lemon wedges.