Flatten chicken to 1/4 inch thickness. Spread with mustard; sprinkle with onion. Place asparagus spears down the center of chicken; fold over and secure with toothpicks if necessary. Place seam side down in an ungreased 8 inch square microwave-safe dish. Sprinkle with cracker crumbs. Microwave uncovered on high 6-8 minutes or until chicken juices run clear. Keep warm
For sauce; in a small microwave-safe bowl, melt butter. Gradually whisk in egg yolks, lemon juice, water and salt. Microwave, uncovered at 30% power for 30 seconds or until mixture reaches 160F and is thickened, stirring once. Spoon over chicken. Sprinkle with almonds. Remove toothpicks.