In a medium bowl, combine the hoisin sauce, coconut sugar, tamari, sriracha, rice vinegar, avocado oil, sesame oil, garlic, and ginger. Whisk until smooth and well combined. Spoon 1/2 cup of the sauce into a small bowl and reserve for glazing and drizzling later.
Place the pork tenderloins in a zip-top bag or shallow dish and pour the remaining marinade over the pork, turning to coat. Cover and refrigerate for at least 4 hours, or up to 24 hours.
Remove the pork from the marinade, shaking off the excess, and transfer to a clean platter. Sprinkle all over with the salt and pepper.
Heat a grill to medium-high heat (350°F to 400°F) and oil the grill grates. To do this, dip a wadded paper towel in a little oil and, using tongs, wipe the oil evenly over the grate. Be careful not to use too much oil, as this can cause flare-ups.
Using tongs, place the pork on the grill. Close the grill and cook for 5 to 7 minutes, then flip.
Meanwhile, toss the broccolini with the avocado oil and a pinch of salt. Place on the grill and cook, turning occasionally, until tender and lightly charred, 4 to 6 minutes. Transfer to a platter.
During the last few minutes of cooking, brush the pork with about 1/3 cup of the reserved hoisin sauce, turning once or twice so it caramelizes evenly. Save the remaining sauce for drizzling over the bowls. Continue to cook, covered, until a meat thermometer inserted into the thickest part registers 145°F to 150°F 5 to 8 minutes more.
Meanwhile, put the remaining reserved marinade in a small saucepan over medium-low heat on the stovetop to warm up while you finish the pork.
Transfer the pork to a cutting board and let rest for 5 minutes before slicing.
Slice the pork into rounds and serve over bowls of rice with the grilled broccolini. Drizzle with the remaining hoisin sauce and garnish with sliced scallions and toasted sesame seeds, if desired.