Bring a medium saucepan of salted water to a boil.
Cook the orzo according to the package directions until al dente.
Reserve ¼ cup of the pasta water, then drain the orzo
Heat olive oil in a large skillet over medium heat.
Add the garlic and cook for about 30 seconds until fragrant.
Stir in the spinach and cook for 2–3 minutes until wilted.
Add the cooked orzo, butter, vegetable broth (or reserved pasta water), lemon zest, lemon juice, salt, black pepper, and red pepper flakes if using.
Toss everything together until well combined.
Stir in the Parmesan cheese until melted and creamy.
Remove from the heat and let the orzo rest for 5 minutes so the flavors meld and the sauce thickens slightly.
Garnish with fresh parsley and additional Parmesan cheese before serving.