• In a nonstick skillet over medium heat, add 2 teaspoons of the oil.
• When the oil is hot, add the onions and saute until translucent and beginning to brown, about 4 minutes. Add the garlic and continue to cook for another 1 minute. Transfer the onion mixture to a medium bowl and allow to cool.
• Heat remaining 2 teaspoons of oil in the skillet and saute the mushrooms for about 6 to 7 minutes. Make sure they are thoroughly cooked. Remove from heat and cool completely.
• Spray a 9x13-inch baking dish with cooking spray.
• Arrange the bread cubes in the dish.
• In a large bowl, beat the eggs, milk, and mustard until incorporated.
• To the eggs, add the mushrooms, onion-garlic mixture, broccoli, cheddar cheese, parmesan cheese, sun-dried tomatoes, salt, and pepper. Stir to incorporate.
• Pour mixture over bread, making sure liquid saturates bread. Cover with plastic wrap and refrigerate overnight, or for at least 8 hours.

When Ready To Bake

• Preheat the oven to 350°F. Remove the plastic wrap from strata and bake, uncovered, for 55 to 60 minutes, or until top forms a light brown crust. Serve immediately.