Add the green beans to a large pot of well-salted boiling water and cook for 3-4 minutes.
Drain and rinse with cold water to stop the cooking and to retain the bright green color. Set aside.
Heat the butter or olive oil in a large skillet over medium heat. Add the mushrooms and cook undisturbed (without stirring) for 3-4 minutes; stir and add the shallots to the skillet.
Cook the shallots and mushrooms for 2 minutes.
Add the minced garlic and green beans, and cook, stirring constantly, for 1 minute or until the green beans are hot. Season with sea salt and pepper to taste.