4 large eggs
2 large egg whites
1.2 tsp fresh ground black pepper
2oz reduced-fat mozzarella cheese, grated (about 1/2 packed cup)
Olive oil cooking spray
5oz spinach leaves (about 5 cups), chopped
2 to 3 cloves garlic, chopped
4 whole-grain sandwich rolls or 8 slices whole-grain bread
1 cup natural jarred marinara sauce

4 large eggs 2 large egg whites 1 2 tsp fresh ground black pepper 2 oz reduced-fat mozzarella cheese, grated (about 1/2 packed cup) 5 oz spinach leaves (about 5 cups), chopped 2 to 3 cloves garlic, chopped 4 whole-grain sandwich rolls or 8 slices whole-grain bread 1 cup natural jarred marinara sauce

In a large bowl, whisk together eggs, egg whites and pepper. Whisk in cheese and set aside. Arrange oven rack in middle position and preheat broiler to high. Mist a broiler-safe, 10-inch nonstick skillet with cooking spray and heat to medium on stove top. Add spinach and cook, sirring occationally until tender, 2 to 3 minutes. Add garlic and toss with spinach until softened, about 1 minute.
Pour eggs over spinach mixture and tilt pan to distribute evenly. When edges start to set, gently lift with a spatula and allow uncooked egg to run beneath. Repeat until liquid no longer runs to the edge, but center of frittata is still wet, about 3 minutes total (lower heat if bottom of frittata is browning too quickly). Transfer to oven and broil until center is no longer jiggly and frittata is cooked through, 2 to 3 minutes (watch carefully to avoid burning). Rest for 5 minutes.
Wearing an oven mitt(skillet handle will be very hot), loosen frittata from pan with a spatula and slide onto a cutting board. Cut into 4 equal pieces to best fit the type of roll or bread you are using. (MAKE AHEAD: Prepare up to 2 days in advance through Step Three; refrigerate in an airtight container.)
Divide frittata pieces among rolls. Serve each sandwich with 1/4 cup of marinara as a dipping sauce. Both frittata and sauce may be served hot or cold.