In a large Dutch oven over medium heat, brown the lean ground beef and chopped onion together, stirring until the meat is fully cooked and the onion is softened. Drain any excess fat to keep the soup lean.

Stir in the diced green chiles, the drained pinto beans, black beans, kidney beans, chicken broth, taco seasoning mix, dry ranch seasoning mix, frozen corn, and diced tomatoes. Mix everything well to ensure an even distribution of flavors.

Bring the mixture to a boil, then reduce the heat to low. Cover and let the soup simmer gently for about 30 minutes, allowing the flavors to blend beautifully.

Ladle the hot taco soup into bowls, top with shredded cheese, and serve with crunchy tortilla chips on the side for added texture and flavor.