Portobello Fresca Melts

Combine the vinegar, soy sauce, 3 tablespoons olive oil, rosemary, grill seasoning, onion, and garlic in a measuring cup or bowl with a spout. Allow it to stand while you wipe the dirt off the mushrooms and place them in a large baking dish, gill side down. Slowly pour marinade over the mushrooms, getting some on each cap. Let them marinate at room temperature for 30 to 90 minutes, occasionally spooning or brushing more marinade over the mushrooms.

While the mushrooms marinate, wash and halve the baby tomatoes. If you’re really short on time, it won’t hurt to leave them whole (they’ll just require a bit more cutting to eat). Just before the mushrooms are done marinating, heat the remaining teaspoon of oil over medium heat in a skillet, then add tomatoes and saute until just softened, no more than 2 minutes. Add the spinach and cook until wilted, then immediately remove from heat and drain off excess liquid (I drained it in a colander then returned it to the pan). Sprinkle with salt and pepper.

Heat grill or grill pan to medium. If using a grill pan, also preheat the oven broiler. Remove mushrooms from marinade, brushing off seasonings, and place them gill side down on the grill pan for 5 minutes. They may stick a little but should release easily with a heat-safe rubber spatula. Turn them over, carefully distribute vegetable filling evenly over the mushroom caps using tongs, and top with cheese. Grill for another 5 minutes, closing the grill lid to melt the cheese. If using a grill pan, heat mushrooms under broiler for two minutes (on a baking sheet) to melt and brown the cheese.

Serve mushrooms with more balsamic vinegar and pepper.

Oven-only method: Instead of heating the grill and the oven, heat only the oven to 450 F (not to broil) and position the rack in the top third of the oven. Line a baking sheet with foil and place the mushrooms gill side down after wiping off the excess marinade. If you have a wire rack or broiler pan, use that so excess moisture drips off the mushrooms. Cook for 5 minutes. Remove from oven, carefully turn to face them with the gills up, then fill with the spinach and tomato mixture and top with cheese. Return to the oven for another 5 to 8 minutes, or until cheese is melted and beginning to brown.