black bean and sweet potato tacos

My sister and I are both completely obsessed with sweet potatoes. For some reason I can't fathom, my dad hates them, so we never have them at home. But now, free from his senseless anti-sweet potato stance, we can have as many as we want! We've mostly been making Asian dishes, inspired by my favorite dish at Chef Jia's, the sizzling Hunan bean curd with yams. But the other day, I decided to change it up a bit by making Mexican food. It turned out delicious. Sadly, we are out of sweet potatoes now, but I plan to get another huge bag as soon as possible.
Sweet Potato Tacos
Serves 1
-1 small sweet potato, cut in half lengthwise
-1/2 an onion,chopped
-1 clove garlic, chopped
-butter or butter substitute (I used Earth Balance)
-2 teaspoons cayenne
-cumin to taste
-1 tortilla, toasted on the stove for a few seconds
-about 1/4 cup black beans
1)Spread some butter onto each 1/2 of the sweet potato and sprinkle each 1/2 with 1 teaspoon cayenne. Bake at 400 until soft (test with a fork), about 40 minutes.
2) Heat up some butter in a non-stick skillet and add the garlic and onion. Cook until onion is very soft, almost caramelized, about 20 minutes. About 10 minutes in, add cumin to taste.
3) Add beans to the onion and garlic and heat them up. Taste it again and add more cumin and cayenne if necessary.
4) Chop the sweet potato into bite size chunks.
5) Put everything together onto the tortilla. You may need 2 tortillas, depending on what size they are.
6) Eat it. This is a very important step, don't forget it!