Σουβλάκια Κοτόπουλο με Λαχανικά και Γρήγορο Τζατζίκι
olive oil, divided, plus extra for the grill (about 45 ml) • balsamic vinegar (about 30 ml) • dried oregano • salt, divided • black pepper, divided • boneless, skinless chicken breast, cut into 24 cubes (about 450 grams) • small zucchini, each cut into 8 thick slices • bell peppers, any color you like, cut into 24 pieces • large onion, cut into 8 or 12 wedges, then halved • nonfat Greek yogurt (about 180 grams) • grated and drained cucumber (about 75 grams) • finely chopped mint •