Preheat your oven to 375 degrees F. Set aside 4 ounces of cream cheese in a tiny bowl (so that when you stuff the meat, you won't dip your utensil that has touched raw meat into your package of cream cheese).
Place the pork tenderloins side by side in a 9x13 pan. Trim off excess fat with kitchen scissors or a knife. Use your knife (a smooth blade works best) to cut a slit into the length of each tenderloin, being careful not to cut all the way through. Wash your hands.
Sprinkle the meat with salt, pepper, and garlic powder (or sprinkle on chopped garlic).
Using a spoon or knife, fill the tenderloins with the cream cheese, making sure to go all the way to each end. Smooth it a bit with your knife or spoon. Wash your hands again, if you touched the raw meat.
To prep your jalapeño, rinse a whole jalapeño and pat it dry. Cut off and discard the stem. With the jalapeño laying on its side, slice it into rings about ¼-inch thick. (Do not touch your eyes once you have cut into a jalapeño, because it will sting.) Use your knife to cut out the membrane and remove the seeds. (If you like extra heat, leave some seeds; use all the seeds for a spicy-hot dish.) Top the cream cheese with your jalapeño slices. Wash your hands well.
Insert a meat thermometer into the thickest part of a tenderloin. Bake the meat, uncovered, for 45 minutes, or until the tenderloin reaches 160 degrees F. Remove the pork from the oven and loosely cover it with foil. Let it rest for 10 minutes before slicing into it, to retain the juices.
While the meat is resting, rinse your cilantro and trim off the stems. Serve the pork sliced, topped with cilantro. Store leftovers in the refrigerator for up to four days.
If you are using cream cheese with chives that comes in a tub, don't buy the one that says "whipped." It will turn out a bit runny. There should be a regular tub of cream cheese with chives. Also, block cream cheese holds up really well in this recipe, but you will need to add your own chives (1-2 tablespoons.) I've used low-fat block cream cheese with good results.