Blue Cheese Portobello Burgers

This is from eatingwell.com. Blue cheese and slow-cooked onions turn a grilled portobello into an indulgent portobello burger. Ruby port—a sweet fortified wine—gives extra depth of flavor to the caramelized onions.

• Ready In: 1 hr
• Serves: 4
• Yields: 4 Burgers

Ingredients

• 3  tablespoons extra virgin olive oil, divided
• 1  tablespoon  balsamic vinegar
• 3  garlic cloves, minced
• 4  large portabella mushrooms, stems removed
• 3  cups red onions, thinly sliced
• 2  tablespoons water
• 1⁄4 cup  ruby port
• 1⁄2 teaspoon salt, divided
• 1⁄4 teaspoon ground pepper, divided
• 1⁄2 cup  reduced-fat blue cheese, crumbled
• 4  whole wheat hamburger buns
• 1  cup baby arugula
• 1  tomatoes, 4 thick slices

Directions

1. Whisk 2 tablespoons oil, vinegar and garlic in a bowl. Brush the mixture all over mushrooms and let stand for 30 minutes.
2. Meanwhile, heat the remaining 1 tablespoon oil in a large skillet over high heat. Add onion and cook, stirring frequently, until beginning to brown, about 5 minutes. Reduce heat to low, add water and cook, stirring frequently, until the onion is browned and very soft, about 15 minutes. Add port; cook, stirring occasionally, until mostly evaporated, about 3 minutes more. Stir in 1/4 teaspoon salt and 1/8 teaspoon pepper. Remove from the heat and cover.
3. Preheat grill to medium.
4. Sprinkle the mushrooms with the remaining 1/4 teaspoon salt and 1/8 teaspoon pepper. Grill, gill-side down, for 5 minutes. Turn over and top each with 2 tablespoons cheese. Grill until the mushrooms are tender, 4 to 5 minutes more.
5. Toast buns. Divide the onions among the mushrooms. Serve (cheese-side up) on buns with arugula and tomato.