Heat cheese sauce via one of the methods located on the pouch.
In medium stockpot, whisk cheese sauce, shredded cheese and hot water. Heat, whisking continually until mixture reaches 165°F until smooth and combined.
To serve: Place two tostadas on serving plate and top 2 ounces of meat on each shell. Drizzle each shell with 1/2 ounce cheese sauce.
Garnish with pickled red onion, cilantro, radishes, jalapeños and green onion, if desired.