Preheat oven to 425°F (220°C). Place sweet potato in an oven-safe vessel and roast until a knife or skewer inserted into its center meets no resistance, about 40 minutes. Remove from oven and allow to cool.
Peel and discard sweet potato skin and mash flesh with a fork in a medium bowl. Add cilantro, pickled jalapeños, and scallions. Stir and fold to combine. Season to taste with salt.
Spread about ½ cup of the mixture evenly over half of 1 tortilla, leaving a ½-inch border. Fold tortilla over and seal edges by pressing down firmly. Repeat with remaining filling and as many tortillas as needed.
Heat 2 tablespoons (30ml) oil in a large skillet or on a griddle over medium heat until shimmering. Carefully add 2 folded tortillas and cook, swirling and moving tortillas around, until golden brown and puffy on first side, about 2 minutes. Flip quesadillas, season with salt, and continue cooking until golden brown and puffy on second side, about 2 minutes longer.
Transfer quesadillas to a paper towel to drain and repeat to cook remaining quesadillas. Serve immediately.
