I absolutely love mushrooms of any kind, especially big meaty portobellos. This recipe is from Bon Appetit which is a great magazine. Here is the original recipe, I made a few changes (and mistakes!) based on what I had on hand. We had this with just a salad, and it was a perfect light meal.
Stuffed Grilled Portobellos
1/4 cup extra-virgin olive oil
2 tablespoons plus 1 teaspoon balsamic vinegar
3 garlic cloves, minced, divided
6 large portobello mushrooms, stemmed
1 1/2 cups panko (Japanese breadcrumbs)
1 cup cubed fresh mozzarella cheese
1/2 cup grated Parmesan cheese
1/4 cup chopped green onions
1/2 teaspoons oregano
1/2 teaspoons thyme
1/4 cup ( 1/2 stick) butter, melted
Whisk oil, 2 tablespoons vinegar, and 1 garlic clove in small bowl for marinade. Using spoon, scrape out gills from mushrooms and place mushrooms on rimmed baking sheet. Brush marinade over both sides of mushrooms, arrange hollow side up, and let stand at room temperature 30 minutes.
Prepare barbecue (medium heat). Mix panko, next 5 ingredients, and remaining 2 garlic cloves in medium bowl. Drizzle butter and remaining teaspoon vinegar (I forgot to add the vinegar...oops!) over panko mixture and toss. Divide panko mixture among mushrooms, leaving 1/2-inch border around edges and packing down slightly. Place mushrooms on grill, stuffing side up; cover grill and cook until cheese melts and juices bubble at edges of mushrooms, rearranging mushrooms occasionally for even cooking (do not turn over), about 6 minutes. I put mine under the broiler at the end to crisp up the stuffing. I also drizzled balsamic glaze once they were done.