Blend flour, salt and pepper into mayonnaise; gradually add milk.
Heat, uncovered, in Microwave Oven until thickened 1.5 minutes; stir. Add cheese and heat, uncovered, in Microwave Oven until melted, approximately 1.5 more minutes. Add onion, pimiento, ham and eggs. Heat, uncovered, in Microwave Oven 2 to 4 minutes or until heated through. Serve on muffins.