Remove the stems from the mushroom and use them as part of the chopped mushroom mixture, below. Using a tablespoon, scrape out the gills from underneath the mushrooms and discard. Combine all the ingredients for the Portobello mushrooms and toss lightly.
In a medium-sized bowl, mix the veal, chopped mushrooms, bread crumbs, milk, garlic powder, onion powder, salt, black pepper and chopped parsley.
Form the meat mixture in 4-6 burgers. Reserve for later use.
Pre-heat the grill; when hot, grill each mushroom until tender, about 6 minutes and reserve warm. Add the burgers one at a time and brown for 2-3 minutes; turn the burgers over and repeat the browning process, making sure the burgers reach an internal temperature of 160°F.
Grill the mushrooms for 3-4 minutes on each side until tender.
Add one slice of Swiss cheese to the burgers.
Place one Portobello mushroom on a serving platter, add a burger and place the second mushroom on top. Serve immediately.
