Place sun-dried tomatoes in small bowl; pour hot water over to cover. Let tomatoes stand until softened, about 15 minutes; drain and slice.
Spray large skillet with cooking spray; heat over medium heat until hot. Saute mushrooms, green onions, and garlic until mushrooms are tender, 5 to 7 minutes.
Add chicken broth and sherry to skillet; heat to boiling. Reduce heat and simmer, uncovered, until liquid is reduced by half, about 5 minutes. Cool to room temperature.
Combine orzo and mushroom mixture in bowl; add tomatoes and remaining ingredients and toss.