Heat a large pan or wok over medium heat and add the vegetable oil. Once the oil is heated and shimmering, add the napa cabbage, bean sprouts, carrots, and shiitake mushrooms. Stirring constantly, cook until the vegetables begin to slightly soften, about 2-3 minutes. 

Add green onion, cornstarch slurry, sugar, salt, and pepper. Stir and cook for another 1-2 minutes. The vegetables should be cooked down, but still have a slight crunch. Remove the vegetable mixture from the heat and set it aside in a large bowl.

Preheat your air fryer to 400 degrees Fahrenheit.

While your air fryer is preheating, prepare your spring rolls. Lay out a single spring roll wrapper, oriented in a diamond shape with a corner facing you. Brush some of the cornstarch slurry along the corner of the top half of the wrapper. 

Scoop about 3 tablespoons of the filling into the center of the wrapper. Fold the lower third of the wrapper over the filling, then fold in both the left and right corners over the filling. It should resemble an envelope at this point.

Continue to roll the spring roll from the bottom up until it forms a baton-like shape. Press down along the seam gently to seal, brushing on more of the cornstarch slurry if needed. Repeat for the remaining spring rolls.

Brush each side of the spring rolls with a thin layer of vegetable oil and place in a single layer in your air fryer basket, allowing roughly ½ inch of space between them. You may need to cook them in batches depending on the size of your air fryer.

Air fry for 12-15 minutes, flipping the spring rolls halfway through. 

In a small bowl, mix together the Thai sweet chili sauce, white vinegar, and chopped cilantro. Taste and add more vinegar for tanginess, more chili sauce for sweetness, or more cilantro for herbaceousness. Serve immediately.