Preheat oven to 350 degrees. Spray a 9-by-9-inch baking dish with nonstick cooking spray.
In a skillet over medium heat, add olive oil, then sauté bell pepper, onion and zucchini until tender. Add garlic and spinach; cook until wilted.
In bowl, beat eggs then add sautéed vegetables, cheese, salt and pepper. Pour the mixture into a prepared baking dish.
Bake 25–30 minutes until fully set. Allow to cool.
Cut into seven strips, then cut down the middle to create 14 pieces.
Refrigerate leftovers in airtight container up to 4 days.
To freeze, place cooled frittata fingers in freezer bag and lay flat until frozen. When ready to eat, microwave 60–90 seconds, or until warmed.