Preheat the oven to 350°F.
Sear the mushrooms: Heat a dry skillet over medium-high. Add mushrooms and ¼ teaspoon salt; stir once midway through and cook until browned and their moisture releases, about 5–6 minutes. Transfer to a plate.
Sauté the aromatics: Lower the heat to medium, let the skillet cool slightly, then add 2 tablespoons butter and 1 tablespoon olive oil. Stir in onion and ¼ teaspoon salt; cook until lightly golden, 8–9 minutes. Add garlic and cook 1 minute more.
Make the chowder: Stir in the Cravings Truffle Corn Sauce, chicken stock, corn, and remaining ½ teaspoon salt. Return mushrooms to the skillet, bring to a boil, reduce to medium-low, and simmer for 10 minutes. Stir in Parmigiano until smooth and creamy.
Roast the salmon: Arrange salmon pieces on a small rimmed baking sheet, leaving space between each. Brush with remaining tablespoon olive oil and season with salt and pepper. Roast until the top is golden and the fish is medium-rare, about 15 minutes.
Serve: Divide chowder among four bowls and top each with a roasted salmon piece. Garnish with scallion greens.
