Prepare spice rub first by combining the brown sugar, coarse salt, cinamon, cumin, pepper and allspice.
Preheat broiler with rack 4 inches from heat.
Line a broiler pan with aluminum foil and place pork on pan, rub all over with oil.
Rub the spice mixture all over the pork, coating it evenly.
Broil, turning occasionally, about 15-20 minutes (thermometer will read 150F).
Meanwhile, make the avocado-pineapple salsa by draining the juice from the pineapple into a small bowl.
Finely chop pineapple and add to the bowl of juice along with the scallions and avocado. Season with a little salt and pepper, toss gently to combine.
When pork is finished, slice thinly and serve with the salsa.
To save the salsa as leftovers, line the bowl with plastic wrap, putting the wrap down into the bowl and directly over the salsa. Then add another piece of plastic wrap over the top, like normal, before refrigerating.