Finely chop 1/2 cup parsley with 1 garlic clove; set parsley mixture aside. Finely chop remaining 2 garlic cloves. Whisk chopped garlic, 4 tablespoons oil and 1/2 teaspoon salt in large bowl to blend. Add mushrooms and toss to coat.
Heat remaining 1 tablespoon olive oil in heavy large skillet over high heat. Add mushroom mixture and saut é until mushrooms are brown and just tender, about 10 minutes. Remove skillet from heat. Mix in parsley mixture and lemon juice. Season to taste with salt and pepper. Transfer mixture to bowl. Garnish with additional fresh parsley and serve.