In a large pot or Dutch oven, heat over medium-high heat. Add the ground beef and cook until it is browned, breaking it apart with a wooden spoon as it cooks. This should take about 5-7 minutes.
Add the chopped onion to the pot with the browned beef, and sauté for an additional 3-4 minutes until the onion is soft and translucent.
Stir in the kidney beans, black beans, corn, diced tomatoes, tomato sauce, and taco seasoning. Mix everything well to combine.
Bring the mixture to a boil, then reduce the heat to low and let it simmer for about 15-20 minutes.
Ladle the soup into bowls and top with shredded cheddar cheese, a dollop of sour cream, fresh diced tomatoes, avocado slices, and a sprinkle of cilantro. Serve with lime wedges and corn chips on the side for dipping.