Saute the onion, garlic, and jalapeno in a heavy pot over medium heat.
Add most of the remaining ingredients, bring to a boil, then simmer.
If you are using raw chicken instead of precooked rotisserie chicken, this is where you add it and let it simmer until cooked through.
Remove from heat and stir in sour cream, shredded cheese, and cooked chicken (or remove and shred the chicken, then return it again)
I like to prep bowls of individual toppings to serve on the table 'family style' so everyone can top their own bowl just the way they like it. I think it's perfect with a few slices of avocado, a little sour cream, and a lime wedge.
But my family loves it with corn chips and extra cheese!
Add everything but the sour cream to the slow cooker. You can saute the onions, jalapenos, and garlic before adding them if desired. Cook on low for 5-6 hours or on high for 3 hours.
Remove the chicken and shred. Scoop out some of the beans and broth, blend them until smooth, then stir back into the soup along with the shredded chicken and the sour cream.