Prick Sweet potatoes with a fork. Wrap in a damp paper towel and microwave on high for 8-10 minutes, depending on the size of your potatoes.
Peel the sweet potatoes and place in a large bowl. Mash with a fork. Mix in salsa, chili powder, lime juice, black beans, salt and pepper, and nutritional yeast.
Spread the sweet potato mixture onto a tortilla. Top with a second tortilla and lightly press it down. Repeat with the rest of the tortillas.
Heat a pan or over medium heat. Cook quesadillas for about 2-3 minutes on each side, until golden brown and grill marks form.