In an ovenproof pan, sautée the onion and mushrooms until tender, then cook the garlic until fragrant. Mix in the green beans, cream of mushroom soup, and half-and-half. Season with salt and pepper to taste.
Fold in ½ cup of the crispy onions. Bake for 30 minutes, or until set.
Top with remaining crispy onions, and bake for an additional 5 minutes. Serve right away.