Preheat the oven to 350°F.
In a large sauté pan, heat the oil over medium heat. Add the onions, carrots, celery and mushrooms, and cook until the liquid has been released and evaporated. Add the spinach and asparagus, and cook until the spinach is wilted. Remove from heat and set aside to cool to room temperature.
Spray a 9 x 9-inch baking dish with vegetable cooking spray.
In a large mixing bowl, whisk together the egg whites, milk, sage, thyme, salt and pepper.
Place the ham, bread crumbs and cooled vegetables in the bottom of the pan and cover with the egg mixture.
Bake for 40-45 minutes, until the center is firm and set.
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