Gather all ingredients.

Bring a large pot of lightly salted water to a boil. Stir in orzo and return to boil. Cook pasta uncovered until partially cooked, about 5 minutes. Drain and rinse with cold water until cooled completely.

Heat olive oil in a large pot over medium heat. Add chopped carrots, celery, and onion; cook until translucent, about 5 minutes. Add garlic; cook until fragrant, about 1 minute.

Season mixture with thyme, oregano, bay leaf, salt, and black pepper. Cook another 30 seconds before adding chicken broth into the pot.

Bring broth to a boil. Reduce heat to medium-low and simmer partially covered until vegetables are tender, about 10 minutes.

Stir orzo, lemon juice, and lemon zest into the broth; add cooked chicken. Simmer until chicken is heated through, about 5 minutes.

Add baby spinach and cook until wilted, about 2 to 3 minutes. Ensure orzo pasta is tender.