In a small bowl, whisk together the soy sauce, brown sugar, grapeseed oil, lime juice, mirin, ginger paste, and garlic. Pour the marinade into a large ziploc bag and add the pork belly to it. Seel, releasing any air, and massage the marinade into the pork belly. Place it in the fridge and marinate for at least 4 hours or up to overnight.
Preheat your oven to 325 degrees F.
Once the pork belly has marinated, remove it from the fridge and remove the pork belly from the bag (make sure to save the marinade). Pat the pork belly dry with paper towels.
To a large enameled cast iron braising pan, or a pan that is oven safe, add the canola oil and set it over medium-low heat. Add the pork belly and sear on all sides until brown and caramelized. This will take a bit of time, about 15 minutes. Remove the pork belly from the pan and set it aside, but leave the pan over heat. Pour most of the fat from the pan into a small bowl (you will use this later), reserving about a tablespoon in the pan.
Add the onion to the pan and season with salt. Cook until the onion is tender, about 5 minutes and then stir in the beer, remaining marinade, and chicken broth. Add the pork belly back to the pan and bring the mixture to a boil. Cover the braising pan with a lid or foil and place it in the oven. Braise the pork belly for 2 hours and then remove the lid and braise uncovered for an additional 1 hour.
During that last hour of braising, prepare your sweet potatoes. Add the diced sweet potatoes to a shallow baking dish or baking sheet. Also add the reserved fat to the pan with the sweet potatoes and toss. If you don't have any fat left or forgot to reserve it, you may use a couple tablespoons of olive oil. Season to taste with salt and black pepper and place the potatoes in the oven to roast. Roast the potatoes until tender, about 30 minutes. Remove from heat and set aside, covered, until you are ready to assemble your tacos.
Once your pork belly has finished braising, remove it from the oven and then from the pan and set it on a cutting board to rest for a couple of minutes. Then cut the pork belly into bite sized pieces.
Assemble your tacos by layering baby kale, sweet potatoes, pork belly, queso fresco and cilantro on top of charred corn tortillas. Serve immediately and enjoy!