Combine first 8 ingredients in a medium bowl, stirring well with a whisk.
Heat oil in a large nonstick skillet over medium-high heat. Add shrimp, and sauté for 3 minutes or until done. Remove shrimp from pan. Add onion and bell pepper to pan; sauté 3 minutes. Add soy sauce mixture, shrimp, and spinach. Reduce heat to medium; cook 2 minutes or until spinach wilts. Serve shrimp mixture over pasta.