In slow cooker, combine boiled pinto beans with bouillon cubes and enough water to almost fill cooker.
Let simmer on Low setting for 8 hours.
In a large skillet, brown beef with salt, pepper and onion.
Drain well and set aside.
Assemble as follows: Top each tortilla with beef mixture, cheese and a ladel of beans with juice from slow cooker. Top with preferred garnishes as desired and serve.