Cut pork tenderloin into 3-4 inch pieces. Sprinkle with salt, pepper, cumin, chili powder, and cinnamon. Rub spices into pork.
Heat olive oil in a large skillet over medium-high heat. Sear pork on all sides until browned, about 2-3 minutes per side. Transfer pork to a slow cooker.
Add water, brown sugar, and chopped garlic to the slow cooker.
Cover and cook on low for 6-8 hours or on high for 3-4 hours, until pork is very tender and easily shreds with a fork.
Remove pork from the slow cooker and shred it using two forks. Return shredded pork to the slow cooker and stir to coat with the sauce.
Serve warm in tortillas with your favorite taco toppings like black beans, cilantro, diced onions, or a squeeze of lime.