To make cilantro-tahini dip, whisk together tahini, broth, tamari and ginger juice.
Stir in cilantro before serving.
For spring rolls, heat oil in a medium skillet and cook portobellos with lime juice and tamari until tender, about 5 to 7 minutes.
Drain and cool to room temperature.
Combine portobellos, rice noodles, cabbage, blanched collards and chopped cilantro.
Add 1/4 cup cilantro-tahini dip; mix well.
Place one inch of water in a large, shallow skillet over low heat.
Place 1 sheet of rice paper in water. Submerge sheet until soft, about 2 minutes.
Remove from water, let excess water drip and place rice paper on flat surface.
Spoon about 1/2 cup of portobello mixture toward bottom edge or corner (if using square sheets), leaving about 1 to 2 inches of a bottom edge.
Fold up bottom corner or edge over filling while tucking in filling.
Roll until about midway then fold sides over filling, pushing in filling to form a tightly secure cylinder.
Repeat to make 12 total spring rolls.
Serve, sliced on the diagonal, with cilantro-tahini dip.