Place the oil in a large pot set over medium heat. Add onion, celery, carrot and bell pepper and cook until softened, about 5 minutes. Mix in the tomato paste and cook 2 minutes more. Mix in the stock, diced tomatoes, turkey and beans. Bring the soup to a simmer. Simmer 20 minutes. Mix in the pesto and heat through 1 to 2 minutes. Season with salt and pepper and the soup is ready.
Note: "Diced" means to cut into 1/4-inch cubes.