Place the carrots into a jar and top with the vinegar, coriander, garlic, and mustard. Stir well and top with a little water until the carrot is covered. Close the jar and shake well. Refrigerate for a few hours before using.
Boil the bratwursts in water or beer for about 20 minutes until cooked through, flipping if needed. Slice in half.
Mix the broccoli with chili flakes and oil in a large bowl. Toss to coat.
Preheat the grill on medium high.
Grill the broccoli to char.
Grill the bratwursts a few minutes per side to brown.
Cut the bread into sandwich sized pieces so that the brats will stick out on both edges. Cut out a piece on top to fit in the fillings.
Place the bratwursts into the bread. Top with broccoli, mustard, and pickled carrots.