Heat the oil in a large nonstick skillet over medium-high heat. Add the sausage and cook, turning often, until browned, about 6 minutes. Transfer the sausage to a bowl.
Add the onion, bell pepper, and garlic to the skillet. Cook, over medium-low heat, stirring occasionally, until the vegetables are softened, about 5 minutes. If the mixture seems dry, add about 1⁄4 cup water to the skillet while the vegetables are cooking.
Return the sausage to the skillet. Add the broth and tomato sauce; bring to a boil. Reduce the heat and simmer, covered, until the sausage is cooked through, about 8 minutes longer. Stir in the spinach. Cook, stirring occasionally, until the spinach just begins to wilt, about 2 minutes. Stir in the couscous. Cover and remove from the heat. Let stand until the liquid is absorbed and the couscous is tender, about 5 minutes.
Fluff the mixture lightly with a fork just before serving.