In a large skillet, heat olive oil over medium heat. Add the chicken pieces and season with salt and pepper. Cook until browned and cooked through, about 6-8 minutes. Remove chicken from skillet and set aside.

In the same skillet, add diced onion and cook until translucent, about 3-4 minutes. Add minced garlic and sliced mushrooms, cooking until mushrooms are tender, about 5 minutes.

Add the orzo to the skillet and stir to combine with the vegetables. Pour in the chicken broth and Marsala wine, bringing the mixture to a boil.

Reduce heat to low, cover, and simmer until the orzo is cooked and has absorbed most of the liquid, about 10-12 minutes.

Return the cooked chicken to the skillet, add fresh thyme, and stir to combine. Cook for an additional 2-3 minutes to heat through.

Remove from heat and stir in butter for added richness. Adjust seasoning if necessary.

Serve warm, garnished with additional thyme if desired.