Heat the oil in a large, high-sided skillet over medium-high heat. Add the onion, ginger and garlic and cook, stirring occasionally, until just tender and lightly browned, about 5 minutes. Add the curry powder and salt and cook, stirring constantly, for 1 minute. Whisk in the yogurt and heavy cream and bring to a gentle simmer.
Add the fish to the pan, and turn it gently to coat with the yogurt mixture. Simmer gently until the fish has cooked through, 8 to 10 minutes. Serve with rice and naan.