In a large skillet, heat olive oil and sauté chopped white onion for about 5 minutes until translucent.

Transfer the sautéed onion to your slow cooker and add the chili beans, drained black beans, corn, tomato sauce, diced tomatoes, and taco seasoning. Stir well.

Place chicken breasts on top of the mixture in the slow cooker, ensuring they are submerged.

Set slow cooker to low for 3-4 hours if chicken is thawed, or 4-5 hours if frozen.

Once cooked, remove chicken and shred it using two forks, then return it to the soup.

Adjust thickness by stirring in water if necessary, and let simmer for another 10-15 minutes.

Serve hot in bowls and top with shredded cheese, sour cream, and crushed tortilla chips.