Grilled Salmon with Veggies

2 red, orange and/or yellow bell peppers, trimmed, halved and seeded

1 medium red onion, cut into 1-inch wedges

1 tablespoon extra-virgin olive oil

½ teaspoon salt, divided

½ teaspoon ground pepper

1 ¼ pounds salmon fillet, cut into 4 portions

¼ cup thinly sliced fresh basil

1 lemon, cut into 4 wedges