Preheat the oven to 350˚F.
Drizzle some oil into a skillet set over medium-high heat and cook the beef or turkey, breaking it up with a spoon until it's no longer pink.
Add enough barbecue sauce to moisten it — or more if you love it saucy.
Transfer the meat to a bowl, add another drizzle of oil and cook the onion until golden.
Slice the whole sheet of dinner buns crosswise, opening it up like a book.
Spread with mayonnaise and top with the meat mixture and onion.
Sprinkle with cheese.
Replace the top buns and bake for 10 to 15 minutes, until warmed through and the cheese has melted.