Mix the tamarind, mustard, mustard powder, and cumin together in a small bowl until it forms a nice paste.
Trim the tenderloin and remove the "silver skin".
Sprinkle with a little salt and a decent amount of pepper.
Rub the mustard paste all over the pork tenderloin.
Broil on high (make sure the meat is a couple, 2 - 3, inches away from the broiler otherwise you're going to be turning a lot to avoid burning).
Turn every couple minutes until tenderloin is cooked through and at your desired temperature about 12 minutes. (The recommended temperature is often 145 degrees but I find I like mine a little less cooked)
Remove from the oven onto a cutting board and tent for 5 - 10 minutes while it finishes cooking and the juices settle.
Serve by itself, over some greens, rice, with some potatoes, whatever floats you've got! Enjoy!