Preheat the grill on medium heat with the lid closed. If your grill has a built in thermometer, you want it at about 350°F. If cooking inside, preheat your oven to the same.
Combine the onion, olives, tomatoes; basil leaves and fish with the garlic simmer sauce in a large aluminum pan. Stir to coat well.
Top with lemon wedges then season with salt & pepper.
Place on grill or in the oven uncovered and cook for 15 minutes, stir and continue roasting another 10 minutes or until the fish are done.
Remove and serve over rice, pasta or by itself. We also served broccoli and cauliflower.