Preheat oven to 350 degrees F.
Remove stems from button mushrooms and set aside mushroom caps. Finely chop the stems. In a nonstick 10-inch saute pan, heat the olive oil over medium-high heat. Add the shallots and saute until translucent, about 1 1/2 minutes. Add the garlic and mushroom stems to the shallots and continue to saute until soft, about 2 minutes. Remove from heat and fold in cilantro and lemon juice. Season with salt and pepper, to taste.
Place mushroom caps on a nonstick baking sheet with the hollow sides facing up. Place 1 mozzarella cube in each cap and cover with 1/2 teaspoon of the shallot mixture. Lightly spray the caps once with olive oil cooking spray. Bake for 10 minutes or until cheese is melted and mushrooms are golden brown. Remove from oven, sprinkle with chopped parsley and serve warm.