Make It Now:

1. Stir together the diced onion, minced garlic, and oil in a microwave safe bowl. Cover with a paper towel (to prevent splatters) and microwave until softened, about 5 minutes. (Alternatively, you can saute them in a pan over medium-high heat, adding the garlic during the last minute of cooking time.) 
2. Pat the pork dry with paper towels, season it lightly on all sides with salt and black pepper. 
3. Place the pork loin, soy sauce, maple syrup, ginger, cayenne, and cooked onion mixture in a gallon-size freezer bag. Seal tightly and toss to combine. (Freezing instructions begin here.)
4. Marinate the pork in the refrigerator for at least 2 hours and up to 24 hours.
5. Transfer the pork and marinade to the slow cooker. Cover and cook for 3-4 hours on low, or until the pork registers 145°F internally. Transfer the pork to a cutting board, tent with foil, and let rest for about 10 minutes.
6. Carefully pour or ladle the juices from the slow cooker into a medium saucepan. In a small bowl, stir together the cornstarch and 2 tablespoons of water until smooth. Add the cornstarch mixture to the pan and bring to a boil over high heat. Reduce the heat to maintain a simmer and cook, whisking, until thickened, about 3 minutes. Remove from the heat. Taste and season with salt and black pepper, if desired. 
7. Cut the pork into 1/2-inch thick slices. Fan them out on a serving platter and drizzle the sauce over the meat. Serve.

Freeze For Later: Follow Steps 1 through 3. Freeze.

Prepare From Frozen: Note: You will need to have cornstarch, salt, and pepper on hand to complete this meal. Thaw the meal completely using one of these safe methods. Follow Steps 5 through 7.