Preheat grill to medium-high. Stir together chili powder, 2 teaspoons salt, and 1/2 teaspoon pepper; sprinkle evenly over pork. Let stand 10 minutes.

Brush grill grates with oil. Grill pork, turning a few times, until charred in places and a thermometer inserted into thickest part registers 140 degrees, 12 to 15 minutes. Transfer to a cutting board. Grill pineapple and onion, flipping once, until charred in places and crisp-tender, 6 to 8 minutes. Transfer to board with pork. Grill tortillas, flipping once, until hot and blistered in places, 30 to 45 seconds each, placing them inside a folded kitchen towel as you go. Let steam a few minutes to soften.

Thinly slice pork and cut pineapple into 1/2-inch-thick pieces; slice onion. Fill warm tortillas with pork, pineapple, onion, salsa, cabbage, and cilantro; serve.