Preheat oven to 350°F.
Dice onion.
Add a drizzle of oil to a skillet and warm over medium heat. Add onion and cook, stirring for about 4 minutes.
Add ground beef and spices, and cook, stirring until no longer pink.
Drain excess grease and stir in mayo, ketchup and pickles. Turn heat to low and cook another 5 minutes.
Lightly grease a baking dish with butter.
Slice rolls in half and remove tops.
Spread sliced cheddar along the bottoms until buns are covered.
Top with beef mixture. Press down and cover with cheese
Cover with bun tops.
Brush with melted butter and sprinkle with sesame seeds.
Bake for 15-20 minutes, until cheese has melted.
Serve with extra ketchup or hot sauce for dipping.
Store leftovers in an airtight container for up to 4 days. Reheat in a frying pan so the bun doesn't get soggy.
