Mix sirloin, onion soup mix and water together. Refrigerate for one hour. Line a cookie sheet with party rye bread. Spread two tsp. of raw meat mixture on top of the bread. Top with horseradish, to liking. Cut Velveeta slices into four squares, place one square on top of each slice of bread. Bake in a 350º oven until cheese melts and is lightly brown. Serve immediately.
Be careful of the melted cheese, it can be very hot.