In your large pot or Dutch oven, melt the unsalted butter over medium heat. Add the finely diced onion and cook until it becomes translucent, about 3-4 minutes. Stir in the minced garlic and sauté for an additional 1 minute until fragrant.
Add the diced chicken to the pot, seasoning it with salt and pepper. Cook until the chicken is browned and cooked through, about 5-7 minutes. Stir occasionally to ensure even cooking.
Sprinkle the flour and Italian seasoning over the cooked chicken and onion mixture. Stir well to combine, cooking for an additional 1-2 minutes to eliminate the raw flour taste.
Slowly add the chicken broth and whole milk to the pot, stirring constantly to avoid lumps. Bring the mixture to a gentle simmer.
Once simmering, add the uncooked orzo and sun-dried tomatoes to the pot. Stir well and let it cook uncovered for about 10-12 minutes, or until the orzo is tender and most of the liquid has been absorbed, stirring occasionally.
Stir in the chopped baby spinach and half of the grated Parmesan cheese. Cook for an additional 2-3 minutes until the spinach is wilted and the cheese is melted and creamy. If desired, add a squeeze of lemon juice and Dijon mustard for extra flavor.
Serve your Chicken Orzo Recipe (One Pot!) hot, garnished with the remaining Parmesan cheese. Enjoy the creamy goodness!