Mix mayonnaise, mustard, 2 teaspoons rosemary and garlic in small bowl.

Spray grill rack with nonstick spray, then prepare barbecue (medium heat). Brush mushrooms all over with olive oil. Sprinkle each with 1 teaspoon rosemary, then salt and pepper. Grill until tender, about 10 minutes per side.

Spread mayonnaise mixture over buns. Place mushrooms and arugula on bun bottoms. Cover with bun tops.

This recipe yields 4 servings.

Per serving: calories, 223; total fat, 10 g; saturated fat, 2 g; cholesterol, 0.