Portobello mushrooms have a meaty, rich, earthy flavor which can carry a meal on its own.
Preheat oven to broil. In nonstick skillet, heat broth or oil and cook shallots, leeks and garlic until tender about 3 minutes. Mix in zucchini, thyme, and parsley and cook another 4 minutes. Add salt and pepper and remove from heat. Cut off stems from mushrooms, scrape out the gills and wipe down with a cloth or paper towel. Brush mushrooms with oil and sprinkle a little salt inside the mushroom top. Broil mushrooms 3-4 inches from heat for 4 minutes each side. Remove and fill with zucchini mixture. Toss breadcrumbs with 1 tablespoon of melted vegan butter and sprinkle on top of mushrooms. Broil mushrooms 2 minutes more to brown the topping.
To remove the gills from portobello mushrooms, hold mushroom cap in your palm and use a spoon to scrape away the gills from the underside.
Couscous makes a great stuffing for Portobello mushrooms because it is so moist.