Fill large bowl about halfway with hot water. Soak each rice paper in water 15 seconds until malleable. Place rice paper on clean work surface. Place four cucumber ribbons in single layer in center of rice paper. Perpendicular to cucumber, add strip of red cabbage, carrots, 1/2 cup basil leaves, 1/3 cup cilantro leaves, 1/3 cup mint leaves and avocado.
To roll, fold edges of rice paper over each end of filling. Working with side of rice paper closest to you, tuck rice paper around filling and roll tightly.
To cut rolls into bites, use sharp knife and gently move it back and forth. Arrange bites on platter. Repeat with remaining rice papers and filling ingredients.
To make sauce: In small bowl, whisk peanut butter, soy sauce, mirin, fish sauce, 1 teaspoon red pepper flakes and lime juice.
Toast 1/3 cup peanuts by placing in dry pan over medium heat. Move peanuts around until fragrant and toasted, 3-5 minutes. Roughly chop and add to sauce.
Serve spring roll bites on large platter with sauce. Garnish with additional herbs, lime wedges, red pepper flakes and peanuts.