Remove the sausage from its casings and add the loose meat to a heated Dutch oven 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 to the pot and sauté until the onion is softened and the corn is heated through, about 10 minutes.
Stir in the dry orzo and chicken broth, bring the mixture to a boil, then reduce heat to medium-low.
Simmer uncovered for about 10 minutes, stirring every few minutes and scraping the bottom to prevent sticking, until the orzo is tender and most liquid is absorbed.
Remove from heat, stir in the packed baby spinach and cover for a couple of minutes until the spinach wilts.
Stir in the grated Parmesan, season with freshly ground black pepper to taste, and serve immediately.