1: Set the oven to 350°F.
2: Mix together the ground beef with the seasonings.
3: In a big Pyrex dish, spread the mustard and the seasoned meat in a single thin layer.
4: Bake for 20 minutes. Remove and discard the liquid.
5: Mix the sauce ingredients together and set aside.
6: In a pan, combine all the tandoori onions ingredients and cook on medium-low heat until caramelized. Set aside.
7: Spray a clean Pyrex dish with cooking spray.
8: Slice the buns open, place the bottom half into the dish, spread some sauce, then the cooked slab of meat, slices of cheese, tandoori onions, and chopped chilies.
9: Spread the remaining sauce on the top half of the buns and place over the sliders.
10: Mix all the butter mixture ingredients and spread with a brush over the buns.
11: Bake again for 15 minutes at 350°F.
12: Remove from the oven, cut, and serve.
