If you have dried black beans, prepare them ahead of time by soaking overnight or for at least 6 hours. Pressure cook for 5-7 minutes in salted water. If using a can, skip this step.
Preheat the oven to 400 F.
Slice sweet potato rounds as thinly as possible.
Mix all ingredients of the sweet potato marinade in a small bowl (olive oil, paprika, chili powder, garlic, pepper, salt). Split to two baking sheets.
Coat sweet potatoes in the mixture. Try to place similarly sized sweet potatoes on the same sheet.
Put the sweet potatoes in the oven. Cut toppings while they are in the oven.
After 10 minutes, flip them using tongs or a spatula.
Put chips in for another 10 min. Process ingredients for the crema in the mean time: avocado, lime juice, yogurt, water, and salt.
Check on sweet potatoes. If they are still not crisp as desired, broil on high for 1-2 min.
Assemble those nachos! Sweet potatoes on the bottom, followed by toppings, more sweet potatoes, more toppings, and finally your avocado crema and some cilantro.
Have a fiesta!