1. Heat the oven to 450°. In an ovenproof pot, heat the oil over moderately high heat. Add the mushrooms and cook until starting to brown, about 3 minutes. Add the scallion bulbs, garlic, and 1/4 teaspoon each of the salt and pepper. Cook until the scallions start to soften, about 4 minutes.
2. Sprinkle the fish with the remaining 1/4 teaspoon each salt and pepper. Put the fish on top of the mushrooms and scallions and transfer the pot to the oven. Roast until the fish is just done, 10 minutes for 3/4-inch-thick fillets. Remove the monkfish from the pot and put the pot on top of the stove. Add the scallion tops and the cream to the pot. Bring to a simmer and continue simmering the sauce until it starts to thicken, 1 to 2 minutes. Serve the fish topped with the sauce.
Fish Alternatives: Thick fish steaks such as halibut or salmon would hold up well to the pan-roasting and taste delicious with this sauce.
Variation: Pan-Roasted Monkfish with Wild Mushrooms and Scallions: Use 1 pound sliced shiitake mushroom caps or 1 pound of mixed wild mushrooms in place of the regular mushrooms.
Wine Recommendation: The meaty textures of the monkfish and mushrooms will be well served by a full-bodied chardonnay from California or Australia. The dish would even go nicely with a light red wine such as a pinot noir from California.