Brown the beef in a skillet over medium heat for 7 minutes, breaking it into fine crumbles until it reaches 160°F.
Stir in the taco seasoning and water and cook for 3 minutes until the liquid clings to the meat.
Layer beef, nacho cheese, 1 tostada, sour cream, lettuce and tomato in the center of each tortilla, leaving a wide bare rim.
Fold the tortilla edge toward the center in overlapping pleats and hold it seam-side down.
Heat the oil in a clean skillet and toast each wrap seam-side down for 2 minutes, then flip and toast for 2 minutes until crisp.