Wash mushrooms gently in cool water or wipe with damp cloth. Remove stems and chop. Saute onion in butter, add chopped stems, pecans, bread crumbs, lemon juice and salt. Mix well. Mound mushroom caps with stuffing. Broil for four minutes, about four inches from heat. Or cook in microwave oven on 100 percent power 2-3 minutes until heated throughout. Makes 12 appetizers.