Remove fat from chicken. In 3 1/2- to 4-quart slow cooker, mix onion, zucchini, carrots, lentils, broth, salt and pepper. Add chicken.
Cover; cook on Low heat setting 5 to 6 hours.
Remove chicken from slow cooker. Use 2 forks to pull chicken into shreds. Return chicken to slow cooker. Stir in mushrooms and tomatoes. Cover; cook on Low heat setting about 15 minutes longer or until thoroughly heated. Sprinkle with basil. Serve with cheese.