In a small bowl, mix 2 teaspoons salt, cinnamon, garlic powder, cumin, and dried mustard together. Rub over the surface of the pork tenderloin.
Place a large skillet over medium-high heat. Add the butter. Once hot, lay the pork tenderloin in the skillet. Sear the pork loin on all sides to seal in the juices, about 8-10 minutes total.
Then move the pork tenderloin and add in the onions. Sauté for 2-3 minutes to soften.
Cover the bottom of a large 6-quart crock pot with the apple wedges, and sprinkle the brown sugar evenly over the apples. Pour in the sautéed onions and sprinkle with the remaining ½ teaspoon salt. Lay the seared pork loin over the top.
Cover the crock pot and turn on low for 6-8 hours, or high for 2-4 hours. Once the apples are tender, dinner is ready. Cut the tenderloin into slices and place on a platter, surrounded by the apples and onions. Sprinkle with parsley and serve warm.
It’s really hard to overcook pork in the crock pot. However, the apples could cook too long and turn to mush… They will still taste good, but will lack texture. If possible, turn off the crock pot while the apples are soft, but still hold their shape.