― I can't brag enough about the taste and flavors that go into this sandwich. The marinade is a must. The end results are as good as this looks. If you have never tried a portobello mushroom on the grill, your missing out..... honestly, calling all mushroom lovers, go out and get some today! ∙ You will be shocked on the steak flavored texture and taste of how delicious these are! ∙ 4 tablespoon balsamic vinegar ∙ 2 cloves minced garlic ∙ 3 tablespoon olive oil [...].