Make the short ribs: Preheat the oven to 325˚. Toss the short ribs with the five-spice powder and a generous pinch each of salt and pepper. Heat the vegetable oil in a large dutch oven over medium-high heat. Add the short ribs and cook, turning, until browned, 10 minutes. Remove to a plate and spoon off all but a thin layer of the drippings. Add the garlic, shallots, ginger, lemongrass, cinnamon and star anise to the pot and cook, stirring, until the garlic and shallots are softened, about 3 minutes.
Stir 2 1/2 cups water, the soy sauce, 2 tablespoons each brown sugar and rice vinegar, 1 tablespoon fish sauce and the chili-garlic sauce into the pot. Return the short ribs to the pot in a single layer. Bring to a simmer, then cover the pot and transfer to the oven. Bake until the meat is very tender, adding up to 1/2 cup more water if the pot is too dry, about 2 1/2 hours.
Remove the short ribs to a plate; discard the bones. Strain the liquid through a fine-mesh sieve into a small bowl or fat separator. Skim or pour off any excess fat, then pour the liquid into a large skillet. Add the remaining 1 tablespoon each brown sugar and rice vinegar and the remaining 1 teaspoon fish sauce. Bring to a simmer and cook until slightly thickened, 5 to 10 minutes. Return the short ribs to the skillet and continue to cook, turning often, until glazed, 4 to 8 minutes.
Meanwhile, make the grits: Combine the coconut milk, 2 1/2 cups water and 1 teaspoon salt in a medium saucepan and bring to a simmer over medium-high heat. Gradually add the grits, whisking constantly. Reduce the heat to medium low and cook, stirring often with a wooden spoon, until tender, 15 to 20 minutes. If the grits seem too thick, thin with water, 1 to 2 tablespoons at a time.
Divide the grits among 4 shallow bowls. Top with the short ribs and pickled vegetables. Sprinkle with cilantro and mint.