2Use a fork or sharp knife to prick the sweet potato in several places. Place on a piece of aluminum foil and bake until the sweet potato is tender and can be easily squeezed, 40 to 60 minutes. (Alternatively, to speed up the process, the pricked sweet potato can be microwaved on High for 1 minute, then carefully transferred to the oven on a piece of foil. Bake until the potato is tender, 25 to 35 minutes.)
3Meanwhile, pour the oil into a medium skillet over medium-high heat. Add the pork and stir-fry until no traces of pink remain and the pork starts to exude juices, about 5 minutes, breaking up any large clumps as you cook. Add the broccolini and stir-fry until the vegetables are barely tender and retain some crunch, 3 to 4 minutes. Add the miso and water; cook, stirring, for 1 minute or so, until a sauce forms. If the mixture seems dry, add up to a few more tablespoons of water, stirring to combine.
