Whisk together the flour, egg whites, milk, salt, and oil in a large bowl until smooth.
Lightly coat a pan with cooking spray and place over medium heat. Pour 1/4 cup of the batter into the skillet. Tilt the pan in a circular motion to allow the batter to spread to the edges. Cook until the bottom is light brown, about 2 minutes. Flip the crepe and place 2 tablespoons of the mixed berries in the center of the crepe; cook another 2 minutes. Fold the crepe in half and remove with a spatula to a serving plate.