How to Make It
Preheat the oven to 350° and butter a shallow 9-by-13-inch ceramic baking dish. In a large skillet, heat the oil until shimmering. Add the mushrooms and cook over high heat, turning once, until golden and crisp, about 5 minutes. Season with salt and transfer the mushrooms to a paper towel-lined plate.
In a small bowl, toss the panko with 1/4 cup of the cheese. In a large bowl, whisk the eggs with the cayenne, 2 teaspoons of salt and 1/2 cup of the cheese. Stir in the Swiss chard and mushrooms. Scrape the mixture into the prepared dish and bake for about 20 minutes, until the eggs are just set around the edges. Sprinkle the panko on top and bake for about 10 minutes longer, until the casserole is set and the topping is lightly browned. Let stand for 10 minutes before serving.