Peel sweet potatoes and cut into large chunks (although the smaller the cut pieces are, the quicker the boiling process will be). Place into a medium pot and fill up with water just until all the sweet potato pieces are covered.
Place the pot on high heat and bring to a boil. Allow to boil for a few minutes, then bring heat down to medium and cover with a lid. Cook for about 15-20 minutes or until the sweet potatoes are tender enough to pierce easily with a fork.
While the sweet potatoes are boiling, begin preparing quesadillas. Empty black beans into colander and rinse with water and drain. Place tortillas on griddle or pan (if making in a pan, you will most likely need to make the quesadillas in batches). Scoop a spoonful of black beans into each tortilla, evenly distributing between all the tortillas. Set the colander aside to use for the sweet potatoes. If making the guacamole see instructions below.
When sweet potatoes are tender, drain in colander. Dice the sweet potatoes into small pieces and then evenly distribute between all the tortillas. Sprinkle a handful of cheese on top and then fold each tortilla in half into a semi-circle.
In Griddle or Pan cook quesadillas about 3-4 minutes on each side. Flip when side is toasted and golden.
Serve warm with salsa, guacamole, sour cream, or a favorite dipping sauce.