Preheat oven or BBQ to 400°F.
Oven: Roast fillets in centre of oven until just cooked through – about 10 minutes
BBQ: Cook fillets over indirect heat (burner directly under meat is low or off, with other burner providing higher heat) until just cooked through – anywhere from 10-15 minutes, depending on the BBQ
Place the diced mango, red onion, cilantro, and the juice of fresh lime in a small bowl.
Serve the mango chutney on top of the fish.