1/4 cup olive oil
1/2 cup chopped onion
1/4 cup chopped fresh basil (or 1 tsp. Dried)
3 large cloves garlic, chopped
1/2 tsp. Rosemary
1/2 lb. cooked and coarsely chopped shrimp
2/3 cup breadcrumbs
1/2 cup Parmesan cheese
1/4 cup mayonnaise
6 large Portobello mushrooms cleaned and gills scraped off bottom and stem removed

Heat oil in skillet and add in onion, basil, garlic and rosemary.  Saute about 3 minutes.  Transfer to a bowl, mix in shrimp, bread crumbs, cheese and mayonnaise.  Season with salt and pepper

Arrange mushrooms, rounded side down, on an oiled baking sheet. Mound shrimp filling in mushrooms, pressing filling to compact lightly. 

Bake at 350 for 30-35 minutes.

Serve hot.