In 4-quart saucepan, heat oil over medium heat. Add sausages and onion; cook 5 to 7 minutes or until lightly browned, stirring to break up sausages. Add zucchini, garlic, and oregano; cook 5 minutes. Transfer sausage mixture to medium-size bowl.
In same saucepan, heat water and salt to boiling over high heat. Add pasta and cook 10 to 12 minutes or until cooked through and most liquid is absorbed. Reduce heat to low; return sausage mixture to saucepan and mix well. Stir in spinach and tomatoes. Transfer to serving bowl.
