Prepare the Filling:
Heat a large pan or wok over medium heat. Add vegetable oil and sauté napa cabbage, bean sprouts, carrots, and shiitake mushrooms until slightly softened (about 2-3 minutes). Stir constantly.
Add the green onions, cornstarch slurry, sugar, salt, and pepper. Stir for 1-2 more minutes. Remove from heat and let cool in a large bowl.
Preheat the Air Fryer:
Preheat your air fryer to 400°F (200°C).
Assemble the Spring Rolls:
Lay a spring roll wrapper on a flat surface in a diamond shape (corner facing you). Brush the top corner with cornstarch slurry.
Place about 3 tablespoons of the vegetable filling in the center of the wrapper. Fold the lower third over the filling, then fold in the left and right corners. Roll from the bottom up to form a cylinder and seal the edges with more cornstarch slurry. Repeat with remaining wrappers.
Air Fry the Spring Rolls:
Brush each spring roll lightly with vegetable oil. Place in a single layer in the air fryer basket, leaving space between each roll.
Air fry at 400°F (200°C) for 12-15 minutes, flipping halfway through.
Make the Dipping Sauce:
In a small bowl, mix the Thai sweet chili sauce, white vinegar, and cilantro. Adjust seasoning to taste.
Serve:
Serve the spring rolls immediately with the dipping sauce.