Add the green beans, mushrooms, onion, and garlic to the slow cooker.
In a small bowl, whisk together the heavy cream, vegetable broth, thyme, salt, and pepper.
Pour the cream mixture over the vegetables and stir gently to coat everything evenly.
Cover and cook on low for 4 hours until the green beans are tender but still hold their shape.
Just before serving, sprinkle the fried onions evenly over the top.