This makes 2 (very large) sandwiches, but is easily doubled/multiplied as needed.
ALTERNATE SUGGESTIONS: Caramelized onions are wonderful in the filling, as well as a little fresh mint. A light sprinkling of coriander and/or cardamom in the melting butter in the skillet adds great flavor to the naan as it toasts.
Cooked bacon and crisped prosciutto are nice additions to the filling, if you’re cool with stepping out of vegetarian territory …