Preheat your oven to 400°F (200°C). While the oven heats, rub the chicken breasts or thighs with 1 tablespoon of the olive oil, dried oregano, paprika, crushed red pepper flakes, kosher salt, and black pepper. Heat the remaining 1 tablespoon of olive oil in a large oven-safe skillet over medium-high heat. When the oil is shimmering, add the seasoned chicken to the skillet and sear for about 3-5 minutes on each side, until golden brown. Remove the chicken from the skillet and set aside.
Using the same skillet with residual oil and browned bits, add the butter and chopped shallot. Cook over medium heat, stirring occasionally, until the shallot becomes fragrant and starts to soften, about 3 minutes. Add the minced garlic and orzo pasta, stirring frequently, and cook for another 2-3 minutes until the garlic is fragrant and the orzo is just turning golden. Pour in the white wine to deglaze the pan, scraping up any browned bits on the bottom. Let the wine simmer for about a minute.
Pour in 1 1/2 cups water to the skillet. Increase the heat and bring the mixture to a boil, then reduce to a simmer and cook for 3-5 minutes, stirring occasionally. Add the heavy cream, Dijon mustard, grated parmesan cheese, baby spinach leaves, and drained sun-dried tomatoes. Stir well until everything is combined and the spinach has wilted. I like to taste and adjust for seasoning here—adding a touch more salt or pepper if needed.
Return the seared chicken along with any accumulated juices from Step 1 to the skillet, nestling the pieces into the creamy orzo mixture. Transfer the entire skillet, uncovered, to the preheated oven. Bake for 10-15 minutes or until the chicken is cooked through and the orzo is tender.
Once the chicken is fully cooked, remove the skillet from the oven. Squeeze the juice of 1 lemon over the chicken and orzo, and sprinkle with fresh rosemary if desired. Serve hot, making sure to scoop up plenty of creamy orzo and sun-dried tomatoes with each portion. For a burst of freshness, I always add the lemon juice just before serving.