Hold back 1/4 of the marinade for use while grilling.
Squeeze out excess air and refrigerate for at least 1 hour; I prefer 2-3 hours.
2.
Combine the salsa ingredients in a bowl.
Toss well.
Season with pepper.
Refrigerate until serving time.
3.
Preheat the outdoor grill to medium -high heat, or a charcoal grill until fire has died down, but coals glow.
Oil the grate (I use a pan that has holes in it especially made for fish and vegetables).
4.
Remove salmon from the marinade and shake off excess.
Discard remaining marinade.
Grill fillets 3-4 minutes on the first side, then flip them and add the chunks of onion, sliced mushrooms and reserved marinade (it should be 1 big pile of food with the onions and mushrooms in the center and marinade over the fish and onions and shrooms).
Cook until fish is no longer translucent in the center, and flakes easily with a fork.
Onions should be crisp-tender.
Serve the salmon with steamed rice and mango salsa.