Wash and cut the stems off the mushrooms (you want a fairly level surface for your eggs). Pat dry.
Place the mushrooms, undersides up, on a parchment lined cookie sheet.
Sprinkle with balsamic vinegar, garlic powder and chopped, fresh rosemary.
Bake at 350 F. for about 20-30 minutes or until the mushrooms are cooked. While they bake, make your eggs.
Remove mushrooms from oven and top with an egg on each mushroom.
Sprinkle with a little extra, fresh rosemary and serve.
Please note that the nutrition data given here is a ballpark figure. Exact data is not possible.