Remove the sausage from its casings and crumble it into a Dutch oven or heavy-bottomed saucepan set over medium-high heat.
Cook the sausage, breaking it up with a wooden spoon, until browned, about 5 minutes.
Add the chopped onion and frozen corn and sauté until the onion is softened and the corn is warmed, about 8–10 minutes.
Stir in the dry orzo and pour in the chicken broth, stirring to combine. Bring the mixture to a boil.
Reduce the heat to medium-low and simmer, stirring every few minutes and scraping the bottom so the orzo does not stick, until the orzo is tender, about 10 minutes.
Remove the pot from the heat, add the packed baby spinach, stir until wilted, then cover for 1–2 minutes if needed to finish wilting.
Stir in the grated Parmesan and season with freshly ground black pepper to taste, then serve immediately.
