Preheat the oven to 400 degrees F.
Heat 1 tsp olive oil in a large oven-safe, cast iron skillet set over medium-high heat. Cut the chicken breasts in half. Place them in a large bowl, add the seasonings and 1 tsp of oil. Massage the chicken well with hands or with tongs to ensure they are evenly coated in seasoning.
When the oil is shimmering, add the chicken. Sear on both sides until golden, about 3-5 minutes per side. Remove the chicken from the skillet, place on a plate to the side.
Wipe any burnt pieces off the skillet if needed. To the same skillet, add the butter and chopped onion, cook until fragrant (about 3 minutes). Add the minced garlic and raw orzo, toasting until lightly golden, about 2-3 minutes. Add the wine and de-glaze the pan. Add 1 1/2 cups broth.
Bring everything to a boil, cook for 3-5 minutes, then add the cream, parmesan, spinach, and sun-dried tomatoes in oil, stirring until the spinach has softened.
Add the chicken back into the skillet, wiggle it into the orzo mix well. Transfer to the oven and cook, uncovered for 15-20 minutes, until the chicken is cooked through. Add any additional Parmesan and balsamic glaze if using. Serve and enjoy hot!