1. Combine oil, lemon juice, minced garlic, salt, and black pepper in a small bowl. Place mushrooms in a 9-by-13-inch pan. Pour marinade over mushrooms, making sure to coat completely. Let stand at room temperature while preparing grill or broiler, about 10 minutes. Heat grill to medium-high. Alternatively, preheat broiler and adjust oven rack 6 inches from broiler.
2. Grill or broil mushrooms until charred and tender, about 4 to 6 minutes per side. Remove from grill. While mushrooms are cooking, place rolls cut side down on grill or in a toaster oven and lightly toast, about 1 minute.
3. Use a quarter of the Boursin for each sandwich, spreading it on the two halves of each ciabatta roll. Thinly slice mushrooms and mound on bottom half of roll, followed by a quarter of the arugula or watercress. Cover with top of roll, cut sandwich in half on the diagonal, and serve.
Source: Hannaford fresh Magazine, September - October 2007