• 3/4 pounds sliced portabella mushrooms
• 1/2 cup extra-virgin olive oil, divided
• 3 tablespoons red-wine vinegar
• 1 teaspoon Dijon mustard
• 10 cups mixed spicy greens such as mustard, arugula, tatsoi, mizuna, and watercress
• 1 cup shaved gruyere cheese

Preheat oven to 425°F with rack in middle.

Toss mushrooms with 3 tablespoon oil and 1/4 teaspoon each of salt and pepper in a bowl. Roast in 1 layer in a 4-sided sheet pan, turning once, until golden-brown and tender, about 15 minutes. Cool mushrooms.

Whisk together vinegar, mustard, 1/4 teaspoon salt, 1/8 teaspoon pepper, and remaining 5 tablespoons oil in a bowl until combined. Toss mushrooms, greens, and cheese with enough dressing to coat.