Heat a large nonstick skillet over medium heat.  Add the oil and onion and cook until softened, about 6 minutes.  Then add the mushrooms and cook for about 2 minutes, and finally the asparagus, garlic, and salt and cook for another 5 minutes.  Set aside.

In a large bowl, whisk together the eggs, milk, mustard, and parsley.

Lightly grease an 8" x 8" pan (if doubling the recipe, use 9" x 13").  Add half of the bread to the bottom of the pan.  Top with half of the asparagus & mushroom mixture and then half of the goat cheese.  Repeat with remaining bread and veggie mixture.  Then pour the egg mixture evenly over the top and add the remaining goat cheese.

Cover in foil and refrigerate overnight (or at least an hour).

When ready to bake, remove the casserole dish from the fridge, take the foil off, and preheat the oven to 375 degrees.  Bake until firm in the center and golden brown on the top, about 45 minutes.  Allow to set for about 10 minutes before serving.