Soft spring rolls are a pleasure to see and to eat and simple to make if you set up a small assembly line with all the components ready to roll up. The secret ingredient here is extra pairs of hands, to make the job interesting and fun.
Combine the ingredients in a small bowl and set aside.
Submerge the rice noodles in a bowl of hot water until soft and clear, 8-10 minutes. Drain and cut the noodles into 2-inch pieces and set aside. Toss the mushrooms with the soy sauce in a small bowl and set aside.
Submerge 1 spring roll wrapper in a shallow pan or bowl of warm water until softened, for about 30 seconds. Remove carefully, draining the water, and place on a work surface. Arrange some smoked salmon slices, cucumber, carrots, avocado, basil, cilantro, red onion, and peanuts in a log shape in the center of the wrapper.
Lift the wrapper edge nearest to you and roll it away from you, up and over the fillings, tucking it in under them compressing everything gently into a cylinder shape, folding the ends to seal. Set the roll aside on a platter, seam-side down to dry. Repeat to make the remaining rolls.
Serve the spring rolls whole or halved crosswise, with dipping sauce.