In 3- to 4-quart slow cooker, mix onions, bell pepper and garlic.
In large bowl, mix cornmeal, chili powder, oregano, cumin and salt. Add chicken; toss to coat. Add chicken and any remaining seasoning mixture to vegetables in slow cooker. Gently stir in picante sauce, beans and tomatoes.
Cover; cook on Low setting 6 to 8 hours. Sprinkle with green onion.