Go to the Recipe: Super-Savory Grilled Portobello Mushroom Burgers
Something that I will do when I'm cooking w/portabello mushrooms is remove as many of the gills that I can. Even with a choice portabello mushroom where the cap is still partially closed, you can take a spoon and scrape out some of the gills. An old grapefruit spoon is useful here if you have one. The gills don't add to the flavor, cook down to nothing, and mainly seem to darken everything as they cook. Particularly if you're precooking them in a microwave.
