01 - Heat a non-stick skillet over medium heat. Add sliced shiitake mushrooms and sauté for 5-6 minutes, stirring occasionally, until tender and slightly caramelized. Set aside to cool completely.
02 - Julienne the carrot and cucumber. Thinly slice the red bell pepper. Slice the avocado just before assembly. Finely chop the scallions. Wash and dry the spinach or lettuce leaves. Pick cilantro and mint leaves from stems. Arrange all ingredients within easy reach for assembly.
03 - Fill a shallow dish with warm water. Dip one rice paper sheet in the water for 10-15 seconds until pliable and just softened. Carefully transfer to a clean, damp kitchen towel or cutting board, smoothing out any wrinkles.
04 - Place a small handful of spinach or lettuce in the center third of the rice paper. Layer with 2-3 avocado slices, a portion of sautéed shiitake mushrooms, carrot strips, cucumber strips, bell pepper slices, scallions, and a sprinkle of fresh herbs.
05 - Fold the bottom edge of the rice paper over the filling tightly. Fold in both sides toward the center, then roll forward from bottom to top, keeping the roll tight and tucking in ingredients as you go. Repeat with remaining ingredients to make 8 rolls.
06 - Whisk together soy sauce, rice vinegar, sesame oil, maple syrup, grated ginger, and minced garlic in a small bowl until well combined. Add water, 1 teaspoon at a time, to achieve desired consistency.
07 - Serve spring rolls immediately, whole or sliced diagonally in half, with dipping sauce on the side. For best presentation, place sliced rolls cut-side up to showcase the colorful filling.