Preheat oven to 375F and grease a 9x13 baking dish.
Bring salted water to a boil, add green beans, and cook 3-5 minutes until bright green.
Drain green beans and set aside.
Heat oil in a pot over medium-high heat, add mushrooms, sprinkle with salt, and cook 8-10 minutes until browned, stirring occasionally.
Remove mushrooms and set aside.
Reduce heat to medium, add butter, then cook shallots and garlic 2-3 minutes until soft.
Sprinkle flour over top, stir well, and cook 2-3 minutes, stirring constantly.
Add cream cheese and stir until melted.
Add broth and bring to a simmer.
Add Worcestershire sauce and half and half, bring back to a simmer.
Stir in nutmeg and parmesan until melted.
Season with salt and pepper to taste.
Stir in blanched green beans and browned mushrooms.
Pour mixture into prepared baking dish and cover with foil.
Bake covered for 15 minutes, then uncover and bake 15 minutes more.
Sprinkle crispy onions over top and bake 5 more minutes.
Let cool 5-10 minutes before serving.