In a small bowl, stir together the cumin, salt and pepper. Sprinkle all over the pork. In a large cast-iron skillet or grill pan, heat the olive oil over medium heat. Add the pork to the pan and cook, turning, until browned and firm to the touch, about 10 minutes. Transfer to a cutting board and tent with foil to keep warm.
Using the same skillet, add the pineapple and cook over medium heat, turning, until golden, about 8 minutes.
Slice the pork. Divide the pineapple, pork and avocado among 4 plates. Top with the jalapeño.