You can prepare this casserole and refrigerate overnight. The next morning, let the casserole stand at room temperature while oven heats and then bake as directed.
To make this plant based, use an egg substitute.
Heat oven to 375 F. Coat a 7-by-11-inch glass baking dish or a 2-quart casserole with cooking spray.
Place the spinach in a strainer and press with the back of a spatula to remove excess liquid. Set aside.
In a medium bowl, whisk together eggs, egg whites and milk. Add dry mustard, rosemary, spice blend and pepper; whisk to combine.
Toss spinach, bread, onion and red pepper in a large bowl. Add egg mixture and toss to coat.
Transfer to prepared baking dish and push down to compact. Cover with foil.
Bake for 30 minutes or until the eggs have set. Uncover and top with cheese. Continue baking for an additional 15 minutes or until the top is lightly browned.
Transfer to a wire rack and cool for 10 minutes before serving.
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