Portobello Mushroom Sandwich

Here is a yummy late summer dinner I made tonight: portobello sandwich, corn on the cob, and spicy watermelon soup. I'll give you the recipe for the sandwich tonight. Corn on the cob is easy (especially if you grew up in Indiana and went to college in Iowa and have eaten sweet corn every late summer day since you were a kid and, no, Pennsylvania sweet corn is nowhere near as good). Unfortunately, I haven't perfected this watermelon soup, so I won't give you all the recipe yet. 

Sandwich time, here goes:

For 2 sandwiches, you'll need:

• 2 portobello mushroom caps
• 2 T balsamic vinegar
• 1 T olive oil
• 2 t grill seasoning (the kind you buy premixed for steaks. Mine has onion powder, garlic, salt, parsley, black pepper, etc.)
• 2 large slices of sourdough bread (or 4 slices if you don't have a big, oblong loaf of sourdough)
• 1 large [heirloom] tomato, sliced
• 1 leaf romaine lettuce, slice in half
• 2-3 T vegan margarine (Earth Balance truly is superior)

The steps:

1. In a shallow tupperware, combine vinegar, olive oil, and seasoning. 
2. Clean and remove stems from mushroom caps.
3. Place mushrooms in tupperware and let marinate for at least 30 minutes. Shake the tupperware occasionally to ensure even coverage.
4. While the mushrooms are marinating, toast the bread in a pan with a bit of margarine until lightly golden, if you'd like.
5. Once mushrooms are done marinating, pour the extra marinade into a skillet along with the margarine and heat until margarine melts.
6. Cook mushrooms over low heat, covered, for about 5-7 minutes, flipping once during the process. Mushrooms are done when they have softened all the way through (check in the center) and the bottoms are a little bit darker.
7. Assemble your sandwiches with lettuce, tomato, and mushroom. I think a light spreading of Vegenaise would be great too.