Preheat a grill to medium high and brush the grates with vegetable oil. Grill the pineapple until well marked, about 2 minutes per side; let cool. Dice the pineapple and mix with the pico de gallo; set aside.
Season the pork with salt, then rub with the chile powder and 1 teaspoon cumin. Grill, covered, turning every 4 minutes, until a thermometer inserted into the center registers 145 degrees F, 12 to 15 minutes. Transfer to a cutting board and let rest 10 minutes.
Meanwhile, combine the farro and 1/2 teaspoon salt in a medium saucepan and cover with water by 1 inch. Bring to a boil, then reduce to a simmer and cook until the farro is tender, 15 to 18 minutes. Drain and let cool.
Make the vinaigrette: Whisk the lime juice, remaining 1/2 teaspoon cumin, 1/2 teaspoon salt and a few grinds of pepper in a medium bowl. Slowly whisk in the olive oil.
Divide the farro, spinach, cabbage and avocado among bowls. Thinly slice the pork and add to the bowls. Season with salt and pepper and drizzle with the vinaigrette. Top with the pineapple salsa.