Make the sloppy joe mixture: Heat a medium skillet over medium high heat and add the beef. Cook, breaking up and stirring occasionally, until almost all the way cooked through and browned. Stir in the taco seasoning, ketchup, brown sugar, and dijon. Cook for 3-5 minutes or until well combined and thickened. Remove from heat and let cool slightly.
Slice the block of buns in half lengthwise. Layer about half of the cheese on the buns. Top with the beef mixture, then with the remaining cheese. Top with the top half of the buns.
In a small bowl, mix together the melted butter, cilantro, and garlic powder. Brush the butter mixture evenly over the top of the buns.
Transfer to the oven and bake until the cheese is melted, about 10 minutes. Serve, pulling apart each slider from the bunch as you go.