Prepare pasta according to package directions, omitting salt and fat. Drain well; return to pan. Stir in spinach; toss well until spinach wilts.
Melt 1 tablespoon butter in a large nonstick skillet over medium-high heat. Add shrimp. Sprinkle with 1/4 teaspoon salt; sauté 2 minutes or until shrimp are done. Remove shrimp from pan; set aside. Melt 1 tablespoon butter in pan over medium heat. Add onion; cook 10 minutes or until tender, stirring often.
Stir in broth, vermouth, and rind. Increase heat to medium-high; cook 8 minutes or until mixture begins to thicken. Reduce heat to medium. Add cheese; stir until well blended. Stir in 1/4 teaspoon salt, nutmeg, and pepper; remove from heat. Add shrimp and onion mixture to pasta mixture; toss to combine.