In a heavy saucepan heat olive oil over medium-high heat. Reduce heat and add carrots, celery and onion; cook until soft and golden brown, 5 to 6 minutes. Add chicken broth, corn, turkey, salt, and pepper; bring to a boil. Simmer soup uncovered for 10 to 15 minutes. Season with salt and pepper. Before serving squeeze in the juice of a lemon.