Place bread in warm oven, 250 degrees F, to dry and toast, 20 minutes.
Place tuna in a skillet and add wine, then water -- just enough to cover fish. Add bay leaf and peppercorns. Bring liquids to a boil. Reduce heat to simmer and cover skillet. Poach fish for 12 minutes.
Heat a large skillet over medium heat. Add oil, 1 turn of the pan, and 2 tablespoons butter--reserve remaining 2 tablespoons butter. Add shallots and mushrooms and season with salt and pepper. Saute gently for 5 minutes. Sprinkle in ground thyme or poultry seasoning and flour and cook flour 1 minute, stirring with whisk. Whisk in stock, then cream. Adjust seasonings. Add peas.
Remove cooked, poached tuna to a bowl and flake fish with a fork.
Add cooked noodles and tuna to sauce. Remove sauce from heat and transfer mixture to a casserole or serving dish.
Use the widest cutting edge on a box grater to grate the bread into large crumbs. Melt remaining 2 tablespoons butter in a small cup in microwave and pour melted butter over bread, Scatter buttery bread crumbs and parsley over the top of the casserole. Serve immediately.