Turn the slow cooker on high heat.
Rinse the pinto beans and remove any floating beans or small rocks.
Add the beans, water, onion, lime juice, cumin and cajun seasoning to the slow cooker.
Cook on high for 5-6 hours (or low for 7-8 hours), stirring occasionally.
After the beans have fully cooked, immediately mash them with a potato masher or immersion blender.
Add salt (start with 1/2 tsp) and increase to taste.
Optional - Top with cheese, sour cream or salsa and enjoy!