Cook orzo according to package directions, omitting salt and fat.
Melt butter in a large nonstick skillet over medium heat. Add shallots and garlic; cook 2 to 3 minutes or until tender. Sprinkle flour over mixture; cook 2 minutes. Slowly whisk in broth; bring to a boil. Add rind, juice, and salt. Simmer 3 to 5 minutes or until thick.
Combine orzo, spinach, cheese, and shallot mixture; stir until blended.