Position a rack in the center of the oven and preheat to 350 F. Spray an 8-inch square baking pan with the cooking spray.
Whisk together the flour, oats, cereal, brown sugar, flaxseeds, baking powder, baking soda, cinnamon, nutmeg and salt in a large bowl to combine them. Whisk together the honey and egg, then add the juice, oil or butter and vanilla. Make a well in the center, add the liquids and stir with a wooden spoon just until combined. Stir in the nuts or seeds and dried fruit.
Spread the batter evenly in the pan. Using a knife, cut the moist dough into thirds. Turn the pan and cut the dough into fifths to make fifteen bars. (Precutting will make it easier to cut through and separate the bars after baking.)
Bake until the top of the pastry is light browned, about 22 minutes. Cool briefly in the pan on a wire cake rack. Following the previously cut divisions, use a large, sharp knife to cut into bars. Remove to a wire rack to cool completely. (The bars can be stored in an airtight container for up to 5 days. To store longer, individually wrap each bar in plastic wrap, place in a ziploc bag and freeze for up to 3 months. Thaw at room temperature overnight.)
Makes 15 Bars