In a 4- to 5-quart slow cooker, combine the first 8 ingredients. Add water or stock and 1 teaspoon of salt; stir to combine.
Cover and cook on low for 10-12 hours or until most of the water has evaporated; let cool and discard the bay leaves.
To make avocado crema, in a blender or food processor, combine yogurt, avocado, lime juice, jalapeno pepper and cilantro leaves; season with salt and pepper to taste and process until smooth.
To serve, mash the beans slightly and set in the bottom of four to six 12-oz glasses. Top with avocado crema, grape tomatoes, queso fresco and red onions. Garnish with cilantro.
Serve with tortilla crisps.
Notes
You will end up with leftover black beans base than 4 to 6. Double the quantities for the other layers if you are serving more guests or refrigerate beans for another use.