In a small bowl, combine the chili powder, paprika, cayenne, cumin, and salt. After you've cut the potatoes, toss them in about a tablespoon of olive oil and the seasoning mixture until well dispersed. Bake on a baking sheet in an oven heated at 350 degrees Fahrenheit on the middle rack until tender, about 45-50 minutes. Flip potatoes about halfway through.
On another baking sheet, place the jalapeno halves open-side up, and wrap the garlic cloves in a small bit of aluminum foil. Place on the top rack of your oven while the potatoes cook. Cook for about 20 minutes, turning once. The jalapeno should be roasted, and the the garlic should be very soft.
Place the black beans, jalapeno, garlic, cilantro, and lime juice in a food processor. Pulse until smooth. While the processor is running, slowly pour in the vegetable oil. Add more if you feel it needs a runnier consistency. Add a pinch of salt.
Heat a medium-sized skillet over medium high heat. Drizzle about a 1/2 tablespoon of olive oil, then toss in the sliced onion. Cook slowly, stirring occasionally, until the onions caramelize to your taste. I cooked mine about 7-8 minutes.
Heat the tortillas in a microwave or skillet. Spread a layer of the black bean mixture in the middle of the tortilla, then top with a spoonful of the sweet potatoes. Top with a bit of onion and a sprinkling of crumbled cotija cheese. Serve with red salsa or avocado as well.