When getting the pork tenderloin ready, check and see if it seems like it has too much silverskin (this is like a membrane that doesn't cook very well and can affect texture). Most store bought pork tenderloins are trimmed enough already, but if there is a lot of silverskin, then carefully remove it. On most store-bought pork tenderloins, even a little leftover silverskin isn't usually an issue.
Place the pork tenderloin into a plastic zipper bag or reusable air tight container that fits the pork snugly along with the marinade of your choice.
Carefully squeeze the air out of the bag and close it up or place the lid on the container. Make sure the marinade is in contact with all parts of the pork. Refrigerate and marinate the pork for at least 4 hours or up to 8 hours.
When ready to grill, remove the pork from the fridge and let it come to room temp for at least 30 minutes, but no more than an hour.
If using a propane grill (the easiest method) or a charcoal grill, the goal is to create zones of heat. One side of the grill needs to be really hot and the other needs to be very low or no heat. On a propane grill set one side of the grill's burners to high heat and the other side to very low heat (on my grill, I have three burners, so I set the left and middle ones to high and left the right side burner on the lowest setting). If using a charcoal grill, pile 75% of the charcoal onto one side and leave just a little bit of charcoal on the other.
When the grill is nice and hot on the hottest zone, place the pork tenderloin on the hot zone letting it sear for no more than one minute per side. The tenderloin usually has 3 or 4 sides that it can rest on without rolling.
Save the marinade in the bag/container to use later if you want to create a glaze for the pork (instructions below)!
After searing, move the pork to the low heat zone of the grill. Make sure the fatter side of the tenderloin is towards the higher heat zone, but not on it. The thinner side of the tenderloin should be as far from the high heat zone as possible. This allows the tenderloin to cook a bit more evenly throughout. Lower the high heat zone to medium-high heat.
Let the pork cook for about 4 minutes per side (again, 3 or 4 sides). After cooking for roughly 12 minutes (rotating every 4 minutes), check the temperature of the thickest part of the tenderloin using a digital meat thermometer. The temperature should read 140 to 145 degrees F.
When the pork is 140 to 145 degrees F in the thickest part of the tenderloin, remove it from the heat and tent it with aluminum foil. The pork will continue to cook a bit, but the goal is an overall internal temp of 145.
Let the pork rest for at least 10 minutes before slicing in order to redistribute the juices.
While the pork rests, pour the saved marinade into a small, shallow, nonstick frying pan. Bring the liquid up to a simmer and then reduce to a low heat. Let the marinade simmer for about five minutes. This will thicken up the marinade and it can be used like a glaze or sauce on the pork when serving. Don't heat it for too long or it will become too thick to use or possibly burn due to the sugars in the marinade. Please note that when reduced, the sriracha marinade is very spicy!
Place the heated and reduced marinade in a small container to use as a dipping sauce or as a topping for the pork.
Slice tenderloin into one-inch thick slices after it is done resting and serve immediately. No matter how well you cook a pork tenderloin, it tends to dry out a bit after some time, so the sooner you eat, the better!
Serve it with your favorite sides like rice or salad and top it with a little of the reduced marinade if you like.