Cook the egg noodles in a large pot of boiling water according to the package directions. Drain and set aside.
Meanwhile, heat the oil in a large skillet over medium-high. Once hot add the chicken and cook for about 6-8 minutes, stirring frequently, until cooked through. Remove from the pan and set aside
In the same skillet over medium-low heat, melt the butter. Then add the onions and allow to cook for 10-15 minutes, or until starting to carmelize, stirring often. Add the garlic and cook for 30 seconds until fragrant.
Sprinkle the flour over the onions and the garlic and cook for 1 minute, stirring to coat. Slowly whisk in the milk and cream, then allow the sauce to simmer until thickened. Stir in the thyme, and remove from heat.
Add the cooked noodles, cooked chicken, and sauce to the bottom of a 9-inch x 13-inch baking dish and stir to combine. Sprinkle the Swiss cheese all over the top of the casserole.
In a small bowl, stir together the panko and melted butter, then sprinkle the bread crumb over the cheese.
Bake for 20 minutes. Then carefully sprinkle the fried onions over the casserole and bake for another 10-15 minutes until the sauce is bubbling and the top is golden.
Remove from the oven and garnish with chopped parsley and thyme before serving warm.