1. In a bowl, stir together the egg, onion, horseradish, oats, salt and pepper; add the chuck and combine the mixture well. Form the mixture into a 5-1/2 by 3-1/2-inch loaf in a shallow baking pan.
2. Spread the ketchup over it and bake in the middle of a preheated 400° F. oven for 30 minutes. Let the meatloaf stand for 3 minutes before slicing.