Pour in the broth (and lemon juice). Bring to a gentle simmer and let the flavors mingle for a minute or two.
Stir in the orzo and cook, stirring occasionally, until al dente and the liquid has mostly absorbed, about 8–10 minutes. If it looks dry, splash in a little more broth or water.
If using spinach, add it now and cook until it just wilts, 1–2 minutes. The greens should stay vibrant and bright.
Remove from heat. Stir in the lemon zest and Parmesan (or your dairy-free alternative) until the sauce comes together and coats the pasta in a glossy finish. If the mixture seems too thick, loosen with a splash of reserved pasta water or broth.
Season with salt and pepper to taste. Fold in the parsley (and sun-dried tomatoes if using) for a fresh, herbaceous lift. Serve immediately with extra lemon zest and a light dusting of cheese, if desired.
