In medium bowl, pour hot water over mushrooms. Let stand about 20 minutes or until soft. Drain mushrooms, reserving liquid. Rinse with warm water; drain. Squeeze excess moisture from mushrooms. Remove and discard stems; cut caps into 1/2-inch strips.
Strain mushroom liquid through fine wire mesh sieve or coffee filter into 4-quart Dutch oven. Stir in broth and garlic. Heat to boiling over medium-high heat. Stir in orzo; reduce heat. Add salmon. Simmer uncovered about 10 minutes or until salmon flakes easily with fork. Carefully remove salmon with slotted spatula; keep warm.
Stir mushrooms, bell peppers, spinach, basil and onions into broth mixture. Cook about 2 minutes or until spinach is wilted and orzo is tender.
Place a piece of salmon in each individual bowl; spoon vegetable-orzo broth over top. Sprinkle with cheese.