Butter the ceramic insert of your All-Clad Slow Cooker. In a large All-Clad skillet, cook the onion, the scallions and the mushrooms in the olive oil over medium heat, stirring until the onion is softened. Add the bell peppers, thyme and salt and pepper to taste, and cook the mixture, stirring, for 10 to 15 minutes, or until all the liquid the mushrooms gives off is evaporated and the peppers are tender. Arrange half the bread cubes in the bottom of the buttered slow cooker, spread half the vegetable mixture over them and sprinkle half the Cheddar and half the Parmesan over the vegetables. Arrange the remaining bread cubes over the cheese, top them with the remaining vegetables, and sprinkle the remaining cheese over the top. In a bowl, whisk together the eggs, milk, mustard, Tabasco, and salt and pepper to taste. Pour the egg mixture evenly over the strata. Cover and let sit for 30 minutes, occasionally pressing down lightly on the top with the back of a large spoon to help the bread absorb the liquid. Cook in the All-Clad Slow Cooker on low for 4 hours, or until it is puffed and cooked through. Remove the lid slightly and continue to cook for an additional 30 minutes.
Recipe courtesy of Gourmet Magazine February 1991, Modified by Crystal Schreck February 2008