Here are some balsamic portabellas for you to try.

Betsy

Cooking Tip: Marinate mushrooms in a little balsamic vinegar and olive oil for a few minutes. Grill or sautÈ for eight to ten minutes.

This one from FAT-FREE archive sounds very good:

Date: Wed, 2 Aug 1995 13:55:11 -0400
From: LaurJill@aol.com

PORTABELLA MUSHROOMS
"This appetizer tastes like filet mignon rather than mushrooms"

6 oz. portabella mushrooms
salt
freshly ground white pepper
Seasoning liquid (for example Balsamic Vinegar, veggie broth)

Season the mushrooms with salt, white pepper and seasoning liquid to
taste and grill over high heat 4 minutes, until soft. Let cool. Marinate at
least one hour in the mixture below, chill before serving.

MARINADE: 3 oz. seasoning liquid, juice 2 limes, 1 clove garlic,
minced, 1 small shallot, chopped, 1 sprig fresh rosemary, chopped
(about 1 tsp.), 1 teaspoon fresh parsley, chopped.

Grilled Portabella Mushrooms
From: Kitchen Cut-Ups - http://www.ksnw.com/recipes/recip113.html

4 large Portabella mushrooms - sliced in 1/2" thick slices
olive oil - as needed
1 jar of roasted red peppers

DRESSING:
1/4 cup extra virgin olive oil
2 tablespoons Balsamic vinegar
1 clove minced garlic
1 tablespoon honey
1 tablespoon chopped fresh basil
1/8 teaspoon black pepper

1. Prepare the dressing at least I hour ahead of time so all the flavors will combine. Cover and store in your refrigerator for use.

2. Light your BBQ grill and get hot. When hot, turn to low-medium setting.

3. Rub the mushroom slices lightly on both sides with olive oil and place on the BBQ grill. Cook for 2 to 3 minutes on each side.

4. Cut some of the roasted red peppers into strips for garnish.

5. Place a small amount of dressing in the center of each plate. On the dressing place the grilled mushroom slices. Top with a couple of roasted red pepper strips and a little more dressing.

GRILLED PORTABELLAS
Categories: Appetizers, Side dish, Vegetarian

Yield: 6 servings

6 ea Whole portabella mushrooms
-- cleaned, stems removed

--------------------------------VINAIGRETTE--------------------------------
1/4 c Vinegar
3/4 c Olive oil
1 ts Sugar
1 ts Salt
1/4 ts Freshly ground black pepper
1 tb Balsamic vinegar
2 ts Lemon juice

Prepare vinaigrette: Combine all vinaigrette ingredients in a lidded
jar. Shake well just before using.

Lay clean mushrooms in a shallow baking dish and pour 1/2 cup of
vinaigrette over it.

Cover and marinate for up to 24 hours, turning the mushrooms once.
When ready to cook, drain dressing; reserve for another purpose.

TO GRILL: Place on grill over warm coals for 5 to 10 minutes, turning
once.

TO BROIL: Place on a baking sheet and set under broiler for 5 to 8
minutes.

TO BAKE: Place baking dish in preheated 425 F oven for about 15
minutes.

NOTE: You may substitute sliced portabellas. However, you may need to
grill them on a piece of foil to avoid breakage. Poke holes in the
foil to assure a good smoky flavor.

Kyra Effren, "The Dallas Morning News" Posted by Karen Mintzias

GRILLED PORTABELLAS
From: Metropolitan Magazine
http://www.sea-east.com/metropolitan/sept96/page34.html

4 medium-sized (about 12 ounces) fresh portabella mushrooms
2 tablespoons butter
2 teaspoons minced garlic
2 tablespoons balsamic vinegar
1/4 teaspoon salt
1/8 teaspoon ground black pepper
1 tablespoon chopped fresh basil or parsley

Preheat outdoor grill or broiler. Separate mushroom caps from stems; set caps aside. Coarsely chop stems to measure 1 cup. In a medium saucepan melt butter. Add chopped stems and garlic; cook, stirring frequently, until stems are tender,
5 to 6 minutes. Stir in vinegar, salt and black pepper; remove from heat. Transfer to the bowl of a food processor with a metal wing blade; process until finely chopped; set aside. Place mushroom caps, rounded side up, on a grill or rack in a broiler pan. Grill or broil 4 inches from heat until mushrooms are hot, 2 to 3 minutes. Turn; spread each mushroom with 1/4 of the chopped mushroom stem mixture; cook until mushrooms are tender, 4 to 5 minutes longer. If desired, serve on toasted rolls with sliced tomato and arugula, watercress or lettuce.

YIELD: 4 portions