Mediterranean Spinach Strata

2 (8-ounce) loaves French bread baguette, cut into 1-inch-thick slices
Cooking spray
1 cup chopped onion
4 garlic cloves, minced
1 (8-ounce) package presliced mushrooms
1 tablespoon all-purpose flour
2 (7-ounce) bags baby spinach
1/2 teaspoon salt, divided
1/2 teaspoon black pepper, divided
3 cups thinly sliced plum tomato (about 1 pound)
1 (4-ounce) package crumbled feta cheese
3/4 cup (3 ounces) grated Asiago cheese, divided
3 cups fat-free milk
2 tablespoons Dijon mustard
1 1/2 teaspoons dried oregano
5 large eggs, lightly beaten
4 large egg whites, lightly beaten
Preparation
Preheat oven to 350°.

Place bread slices in a single layer on a baking sheet. Bake at 350° for 12 minutes or until lightly browned.

Heat a large nonstick skillet coated with cooking spray over medium-high heat. Add onion, garlic, and mushrooms; sauté 5 minutes or until tender. Sprinkle flour over mushroom mixture; cook 1 minute, stirring constantly. Add 1 bag of spinach; cook 3 minutes or until spinach wilts. Add remaining spinach; cook 3 minutes or until spinach wilts. Stir in 1/4 teaspoon salt and 1/4 teaspoon pepper.

Place half of bread slices in bottom of a 13 x 9-inch baking dish coated with cooking spray. Spread spinach mixture over bread. Top with tomato slices; sprinkle evenly with feta and half of Asiago cheese. Arrange remaining bread slices over cheese. Combine 1/4 teaspoon salt, 1/4 teaspoon pepper, milk, and remaining ingredients, stirring well with a whisk. Pour over bread; sprinkle with remaining Asiago cheese. Cover and chill 8 hours or overnight.

Preheat oven to 350°.

Uncover strata; bake at 350° for 40 minutes or until lightly browned and set. Serve warm