If you have a food processor, use it to shred the cabbage and carrot. Otherwise, slice the cabbage thinly and slice the carrot into sticks as small as you can get them.
Cut the bell pepper and avocado into thin slices.
Thinly slice the green onion.
Coarsely chop the cilantro, basil, and mint, and mix together.
Cut the cucumbers into thin slices, lengthwise.
Cut the tofu into thin slices, and rip the butter lettuce into pieces about the size of half of the palm of your hand, if using.
At this point, I'd recommend putting each ingredient into a bowl to make assembly easier.
Fill a large bowl with warm (almost hot) water.
Soak a piece of rice paper in the water for 10-15 seconds, until it turns from feeling like a starchy paper to feeling like a piece of fabric.
Lay the rice paper out on your work station and fill with toppings.
Fold the bottom of the rice paper up to cover some of your ingredients. Fold the top flap down, and then roll the side over like a burrito (see the images above for a visual).
Repeat for the rest of the summer rolls!