Pork Souvlaki with Tzatziki

Name: Pork Souvlaki with Tzatziki
Ingredients: 1 1/4 pounds trimmed pork shoulder, cut into 3-by- 1/2-inch strips; 1 large onion, cut through the root end into 1/2-inch wedges; 1/4 cup plus 2 tablespoons extra-virgin olive oil; 3 tablespoons fresh lemon juice, plus lemon wedges for serving; 2 tablespoons chopped fresh oregano; 2 garlic cloves, mashed to a paste; Kosher salt and freshly ground pepper; 1 cup Greek-style whole-milk yogurt; 1/2 European cucumber, seeded and finely diced; 2 tablespoons chopped fresh mint; Warm pita, for serving