Spray the inside of the slow cooker with nonstick cooking spray, or rub it lightly with a little oil.

Place the pork tenderloin in the bottom of the slow cooker, laying two smaller tenderloins side by side if using them, and tuck the skinny ends underneath slightly.

In a medium bowl, whisk together the dry onion soup mix, condensed cream of mushroom soup, and beef broth until mostly smooth.

Pour the onion soup mixture over the pork, spreading it around so the meat is mostly covered, then put the lid on the slow cooker.

Cook on LOW for 4 to 6 hours, or on HIGH for 2 1/2 to 3 1/2 hours, until the pork is tender but still holds together for slicing and the thickest part reaches at least 145°F.

Transfer the cooked pork to a cutting board and let it rest for about 5 minutes.

While the pork rests, stir the sauce in the slow cooker until it resembles golden-brown onion gravy with soft onion bits throughout.

Slice the pork into roughly 1/2-inch medallions, return the slices to the slow cooker, and gently turn them in the warm gravy until coated; serve with mashed potatoes, buttered egg noodles, rice, or cauliflower rice.