Heat 1 tablespoon olive oil in a large skillet over medium-high heat. Add the sausage, breaking it up with a wooden spoon until crumbled. Cook for 5-7 minutes until browned and cooked through.
Add the finely chopped onion to the skillet with the sausage and cook for 3-4 minutes, stirring occasionally, until the onion has softened and become translucent.
Stir in the minced garlic and cook for 1 minute until fragrant. Pour in 8 fluid ounces chicken broth, 8 fluid ounces water, and 1 cup orzo. Season with 1/4 teaspoon black pepper.
Bring the mixture to a boil, then reduce the heat to low, cover the skillet, and simmer for 10-12 minutes, stirring occasionally, until the orzo is al dente and most of the liquid has been absorbed.
Remove the skillet from the heat. Stir in the fresh baby spinach, one handful at a time, allowing it to wilt into the hot orzo. Fold in 1/4 cup grated Parmesan cheese until the sauce becomes creamy.