Mix the spices together and coat the pork tenderloin in an even layer, rubbing it into the meat all over. Leave at room temperature for 30 minutes while you heat outdoor grill on high.
Mix the onions and peppers with salt and pepper. Arrange in an even layer onto a vegetable grill tray.
Once the grill is ready, add the pork, onions and peppers. Cover the grill.
Add the pork and cook 15 minutes, turning every 5 minutes until the internal temperature is 140°F using a meat thermometer.
At the same time you turn the pork, toss the vegetables until they get a little char. If they cook faster than the pork, move them off the grill and cover with foil.
Once the pork is done, remove from the grill and allow to sit for 10 minutes before slicing.
While the pork is resting, warm the tortillas on a cooler side of the grill, a couple of minutes per side.
When the pork has rested slice into ¼ inch slices. Add sliced pork, onions and peppers to a tortilla. Top with avocado slices and cilantro.