|Balsamic vinegar||2 Teaspoon|
|Olive oil||3 Tablespoon|
|Fresh thyme leaves||1 Teaspoon|
|Coarsely ground black pepper||1⁄4 Teaspoon|
|Portobello mushrooms||4 Medium|
|Mayonnaise||1⁄3 Cup (5.33 tbs)|
|Green onion||1 Small, minced|
|Arugula||1 Bunch (100 gm)|
In glass baking dish, just large enough to hold mushrooms in a single layer, mix chicken broth, olive oil, vinegar, thyme, 1/8 teaspoon salt, and 1/8 teaspoon pepper.
Add mushrooms, turning to coat.
Let stand 30 minutes, turning occasionally.
Meanwhile, from lemon, grate 1/2 teaspoon peel and squeeze 1/2 teaspoon juice.
In small bowl, stir lemon peel, lemon juice, mayonnaise, green onion, remaining 1/8 teaspoon salt, and remaining 1/8 teaspoon pepper.
Prepare outdoor grill or heat 10 inch grill pan over medium heat until hot.
Add mushrooms and cook about 8 to 10 minutes per side, turning occasionally and brushing with remaining marinade, until mushrooms are browned and cooked through.
Cut each bun horizontally in half.
Spread cut sides of buns with mayonnaise mixture; top with arugula leaves.
Place warm grilled mushrooms on bottom halves of buns; replace top half of buns to serve.