Tomato & Spinach Dinner Strata

Coat a 7-by-11-inch (or similar-size) baking dish with cooking spray.

Heat 2 teaspoons oil in a large nonstick skillet over medium heat. Add onion and cook, stirring often, until softened but not browned, 5 to 8 minutes. Transfer to a bowl. Add the remaining 2 teaspoons oil to the pan; increase heat to medium-high. Add mushrooms and cook, stirring, until the moisture has evaporated, 4 to 5 minutes. Transfer to the bowl with the onions, add 1/4 teaspoon pepper and salt and stir to combine.

Combine ricotta, spinach, nutmeg and the remaining 1/4 teaspoon pepper in another bowl.

Spoon 1 cup marinara sauce into the prepared baking dish. Break each slice of bread into 4 roughly equal pieces; arrange half the bread on the sauce (the bread doesn't have to completely cover the sauce). Spoon the ricotta mixture over the bread. Arrange the remaining bread over the ricotta. Scatter the mushroom mixture over the bread. Top with mozzarella. Spoon the remaining marinara sauce over the top. The pan will be very full.

Whisk eggs and milk in a small bowl. Pour the mixture slowly over the casserole, poking the filling gently with the tip of a knife until the egg mixture is evenly distributed and the bread is saturated. Coat a piece of foil with cooking spray on one side and cover the casserole, sprayed-side down. Refrigerate for at least 2 hours or up to 1 day.

Preheat oven to 375 degrees F. Bake the strata, uncovered, for 40 minutes. Sprinkle with Parmesan and bake until puffed and golden brown, 10 minutes more. Let stand for 10 minutes. Serve sprinkled with parsley.