In 5- to 6-quart Dutch oven, heat olive oil over medium-high heat. Season chicken with lemon pepper, salt and black pepper. Cook chicken in oil 5 to 7 minutes, stirring occasionally, until chicken is no longer pink. Remove chicken to plate; cover and keep warm.
Add garlic to Dutch oven; cook 30 to 60 seconds, stirring constantly, until fragrant and lightly browned. Add chicken broth and spaghetti; heat to boiling. Reduce heat to medium; simmer uncovered 13 to 15 minutes, stirring occasionally, until most of liquid is absorbed and pasta is al dente.
Stir in ¼ cup of the Parmesan, the butter, lemon juice, lemon peel and cooked chicken. Remove from heat. Gradually add spinach; stir just until starting to wilt. Let stand 5 minutes before serving. Serve warm with remaining ¼ cup shredded Parmesan cheese.
