Add all ingredients to a slow cooker, and stir to combine. Cook for 3 hours on high heat or 6 hours on low heat.
Meanwhile, make the baked tortilla strips. Preheat the oven to 375 degrees F. Brush both sides of the corn tortillas gently with vegetable oil. Stack the tortillas on top of each other and cut into thin strips. Spread the strips in a single layer on baking sheets and season with salt. Bake for 7-10 minutes, or until tortilla strips are crispy. Remove from oven and let cool.
Serve the soup warm with baked tortilla strips and desired toppings.
Note-This soup will keep in the refrigerator in a sealed container for up to 4 days or freeze it for up to 2 months in a freezer container.