Saute hamburger and onion together until cooked. Drain. Combine hamburger, taco seasoning, ranch dressing mix, beans, hominy, green chilis, rotel and diced tomatoes in large crock pot. ( Do NOT drain any of the canned items). Cover and cook on low all day in crock pot.
Top each individual serving with grated cheese, dollop of sour cream, sliced avocado and corn chips.