Peel and quarter onion.
Place dry beans, onion, garlic, salt, cumin, and water into a slow cooker.
Cover and cook on high for 6-8 hours. Be sure to check the water level from time to time; if it gets too low add more water.
Strain cooked beans, reserving the liquid.
Mash beans with a mixer or potato masher, adding in the reserved water as needed until desired consistency is reached.
Dice tomatoes, shred lettuce and cheese (if needed), and slice pears.
Spread an even layer of beans onto each tortilla, then sprinkle with tomatoes, lettuce, and cheese.
Serve with sliced pears on the side.