Step 1: Season the chicken pieces with salt, pepper, and oregano. Heat olive oil in a large skillet over medium-high heat.
Step 2: Add the chicken to the skillet and sear until golden brown on all sides (about 5-7 minutes). Remove chicken and set aside.
Step 3: In the same skillet, add the diced onion and sauté for 3 minutes until softened. Add the minced garlic and cook for another 1 minute until fragrant.
Step 4: Add the dry orzo to the skillet. Stir constantly for 2 minutes to toast the pasta slightly.
Step 5: Slowly pour in the chicken broth, using a wooden spoon to scrape up any browned bits from the bottom of the pan.
Step 6: Return the seared chicken to the skillet. Bring the mixture to a boil, then reduce heat to low and cover.
Step 7: Simmer for 10-12 minutes, or until the orzo is tender and most of the liquid has been absorbed.
Step 8: Remove from heat. Stir in the lemon juice, lemon zest, Parmesan cheese, and baby spinach until the spinach is wilted and the sauce is creamy.
Step 9: Serve immediately with an extra sprinkle of Parmesan if desired.