Sprinkle the lemon juice over the avocado to prevent from turning brown as soon as it is sliced. Place a sheet of nori on a sushi mat. Place a lettuce leaf on top. Lay several strips of avocado, cucumber and bell pepper lengthwise across the lettuce leaf. Sprinkle a few sunflower seeds on top. Sprinkle with several drops of ume plum vinegar on the vegetables. With cold water, very lightly moisten the end of the nori sheet furthest away from you. This will help seal the nori around the vegetables when rolled. Roll up in a jelly roll fashion. Wrap the sushi mat around and very gently squeeze for 2 or 3 seconds to seal the nori. Remove the mat. With a slightly moisten knife, slice the roll in half. Slice each half in half. Slice each quarter in half and place on a serving platter. Repeat with remaining ingredients until all three rolls are finished.
Yields: 24 equal size pieces of sushi
Per serving - 156 calories, 12 g fat (3% calories from fat), 4 g protein, 9 g carbohydrate, 5 g fiber, 0 mg cholesterol, 65 mg sodium