Grill seasoned steak to desired doneness, remove from grill, tent with foil to completely rest. Slice cooled down grilled steak thinly against the grain, set aside.
In deep, large saucepan or dutch oven, fill 2/3rds full with oil. Heat over medium heat while preparing rest.
On flat griddle, melt butter over medium heat. Add veggies and sauté until crisp-tender. (*Season with seasoned salt and pepper if desired.) Add sliced steak, and continue sautéing, tossing with 2 spatulas, until meat is seared.
Top with a nice pile of cheese, and cover with a dome lid or tented foil and cook until cheese is mostly melted. Then set aside, covered with lid.
Carefully cook each naan bread using 2 pairs of tongs. Slowly submerge chalupa shell, (one at a time), into the hot oil, fold like a taco, and fry for a few seconds until deep golden browned. Remove to a wire rack placed over a baking sheet inverted to drain.
When cooled own for a few seconds, with a large spatula, pile cheesesteak mixture into your shells.
Depending on size of steak, one should yield 3 - 4 chalupas.
Dig in and enjoy!