Soak the onions in a bowl of cold water for 10 minutes. Then drain and pat dry on paper towel.*
To make the cranberry salsa, in a medium bowl combine the cranberries, drained onion, chilli, olive oil and lime juice and toss thoroughly to combine, then carefully toss through the avocado and coriander leaves. Check the seasoning and set aside while you cook the salmon.
Preheat a barbecue grill to medium high heat. Cook the salmon on the hot barbecue for about 3 minutes each side or until cooked to your liking.
Transfer the salmon onto four warmed plates, and spoon over the salsa. Serve with lime wedges.
*Note: Red onions can vary in their intensity, if you make the salad and the onion is too strong add extra lime juice to soften the flavour.