In a large bowl, whisk the EVOO, vinegar, 1 tbsp. oregano, kosher salt and pepper. Add the onion wedges; toss to coat. Let marinate, turning once, 1 hour. .
Preheat a grill to medium-high. Arrange the onions on the grill (reserve marinade). Grill, turning once, until softened and lightly charred, 8 to 10 minutes. Return the onions to the marinade, cover with plastic and let stand 10 minutes.
Toss the pine nuts and raisins with the onions; season with salt and pepper. Garnish with the remaining 2 tsp. oregano.