To prepare the marinade, combine the lime juice, chili powder, garlic, and cumin in a zip-close plastic bag; add the pork. Squeeze out the air and seal the bag; turn to coat the pork. Let stand 10 minutes or refrigerate, turning the bag occasionally, up to 2 hours. Drain, reserving the marinade.
Heat the oil in a large nonstick skillet over medium-high heat. Add the pork and saute 3 minutes; transfer with a slotted spoon to a heatproof plate.
Return the skillet to the heat and add the chilies, onion, and salt. Cook, stirring, until nearly tender, about 8 minutes. Add the pork and its juices, pineapple, and reserved marinade. Cook, stirring until the pineapple is softened and the pork is cooked through, about 5 minute.
Meanwhile, heat the tortillas according to package directions.
To serve, spoon a generous 1/3 cup of the filling into each tortilla and roll up to close.