Preheat oven to 350 degrees F

Melt 1 tbsp of butter in a large skillet over medium low heat, add in the onion, brown sugar and salt, stir and cook until soften, 5 to 10 minutes, remove to a bowl and set aside

Place the bottom of the rolls in a baking dish, lay out 6 slices of cheese over the roll bottoms

place roast beef on rolls, spoon the onions over each roast beef slice

Lay out the remaining cheese over the top of those, place the tops of the roll on top of the cheese

Melt remaining butter and brush over the tops of the rolls, sprinkle with the oregano

Place in the oven and bake for 10-15 minutes or until cheese is melty and great