Heat oven to 350°F. Separate dough into 5 biscuits; press each into 4-inch round. Place 2 inches apart on large ungreased cookie sheet. Bake 12 to 15 minutes or until golden brown.
Meanwhile, microwave spinach as directed on box. Drain well; set aside.
In 12-inch nonstick skillet, cook bacon until crisp; drain on paper towels. Reserve 2 tablespoons bacon drippings; set aside. Reserve 5 bacon slices.
Chop remaining 5 bacon slices. In same skillet add bacon drippings, chopped bacon, onions and mushroom stems; cook over medium heat 2 to 3 minutes or until onions are crisp-tender, stirring occasionally. Stir in spinach, chicken, 1/4 teaspoon salt and 1/4 teaspoon pepper; cook 2 to 3 minutes or until thoroughly heated.
Line large cookie sheet with parchment paper. Place mushrooms on cookie sheet, top sides down; spoon chicken mixture on mushroom caps. Bake 14 to 18 minutes or until mushrooms are tender. Remove from oven; top each with cheese slice. Bake 2 to 5 minutes longer or until cheese is melted.
Split each biscuit horizontally. Place one mushroom on bottom half of each biscuit; top with reserved bacon slice and top half of biscuit. Garnish with additional chopped green onions, if desired.