PREPARATION:

1. Lightly spray 13X9-inch baking dish with nonstick cooking spray. Preheat oven to 375°F. Brush dirt from mushrooms; clean by wiping mushrooms with damp paper towel. Pull entire stem out of each mushroom cap.
2. Cut thin slice from base of each stem; discard. Chop stems.
3. Cook bacon in medium skillet over medium heat until crisp. Remove bacon with tongs to paper towel; set aside. Add mushroom stems and onion to hot drippings in skillet. Cook and stir until onion is tender. Add spinach, pimientos, lemon juice and lemon peel; blend well.
4. Stuff mushroom caps with spinach mixture; place in single layer in prepared baking dish. Crumble bacon; sprinkle over tops of mushrooms. Bake 15 minutes or until heated through. Garnish, if desired. Serve immediately.