Heat a large, dry cast iron skillet up on high heat. Place the onions cut-side down into the skillet and cook until charred, about 5 minutes, flip and cook and additional 2-3 minutes until charred.. Once done, pull the onions halves apart and place in the bottom of a 7 quart slow cooker.
Heat a separate small pan (not cast iron - it burns the spices too quickly) on medium-high heat and cook the anise seeds, stirring constantly until dark brown and fragrant, about 2-3 minutes. Remove from the pan into a small bowl.
Add in the cinnamon, coriander and cloves and cook, stirring CONSTANTLY until the spices really darken (but not burn!) and are fragrant, about 1-2 minutes. They burn quickly, so watch them closely. Transfer to a separate small bowl.
Dump the toasted anise seeds onto a cutting board. Use the edge of a drinking class to crush the seeds until broken down. Add the crushed seeds, along with the coconut sugar, red pepper flakes and sea salt into the bowl with the remaining toasted spices.
Cut the large fat-cap off the pork. Rub the spice mixture evenly into the rest of the pork, covering evenly.
Sprinkle the garlic, ginger, fish sauce and lime juice over the onions. Place the spice-rubbed pork on top.
Cover the slow cooker and cook on low for for 8-10 hours.
Once cooked, remove the pork to a cutting board. Then, remove the onions and set aside separately for later use.
Shred the pork with two forks, and then put back into the slow cooker and toss to coat in all the juices. You will have a lot of juice left over, that's normal.
To make the sauce:
Heat a cast-iron skillet up on high heat. Place the jalapenos into it, cut-side down, and cook until charred.
Add the charred jalapenos, along with the ginger, and lime juice into a SMALL food processor (mine is 3 cups) and pulse until the jalapenos are broken down.
With the food processor running, stream the olive oil in until the mixture thickens.
Add in a pinch of salt, along with the cilantro and mint and pulse until the herbs are broken down.
Spread 1/2 Tbsp of sauce on each side of the bun (about 1 Tbsp total per bun.) Then, divide the pork between the buns, followed by the cooked onions and a sprinkle of bean sprouts.