In a large skillet, melt the butter over medium heat.
Add the minced garlic and sauté for about 1 minute, until fragrant but not browned.
Add the sliced mushrooms to the skillet and cook for 5-7 minutes, stirring occasionally, until they are tender and lightly browned.
Stir in the green beans, salt, and pepper. Cook for an additional 5-7 minutes, until the green beans are bright green and tender-crisp.
Remove from heat and drizzle with lemon juice. Toss to combine.
Garnish with chopped parsley if desired and serve warm.