Sauté: Heat olive oil in a large skillet over medium heat. Sauté onion for 3-4 minutes until soft.
Brown: Add mushrooms and cook for 5-7 minutes until golden brown. Stir in garlic for 1 minute.
Toast: Stir in dry orzo and toast for 2 minutes until fragrant.
Simmer: Pour in 2 cups of broth. Bring to a boil, then cover and simmer on low for 10-12 minutes.
Wilt: Stir in spinach until wilted (2-3 mins). If too dry, add remaining 0.5 cup broth.
Finish: Stir in Parmesan and seasonings. Garnish with parsley and lemon zest.