Preheat oven to 400 degrees. Remove stems from mushrooms (save for another use); place caps in a large bowl. Add 1/4 cup oil, 2 teaspoons garlic, salt and pepper; toss to coat. Transfer to a shallow pan; roast, rounded side up, until lightly cooked, about 8 minutes; remove from oven.
Prepare the stuffing: Cook the broccoli rabe in boiling water for 12 minutes; drain well. Finely chop (makes about 1 1/4 cups); place in a medium bowl. In a large skillet over medium heat, cook the pancetta until crisp, 4 to 5 minutes; remove from skillet; chop coarsely; place in bowl with broccoli rabe. Pour off all but 1 tablespoon oil from the skillet; add onion; saute, stirring frequently, until lightly browned, about 5 minutes; add to bowl; add Asiago; mix well.
Turn mushrooms cavity side up. Spoon stuffing into mushroom caps. In a small bowl, combine bread crumbs, parsley, pine nuts; remaining olive oil and garlic; mix well. Sprinkle over stuffed caps. Bake until browned, about 8 minutes. Serve warm. YIELD: 18 portions
Per Portion: 117 Calories (64.9% from fat); 9g Fat (2g Sat, 5g Mono, 1g Poly); 6g Protein; 5g Carbohydrate; 1g Dietary Fiber; 11mg Cholesterol; 446mg Sodium. Food Exchanges: 1/2 Lean Meat; 1/2 Vegetable.