Preheat the oven to 400°F. Spray 4 individual ramekins with oil, or for one large crisp, spray the bottom and sides of an 8-inch or 9-inch square baking dish.
Empty the oatmeal packet into a mixing bowl and mix in the flaxseed. Place about one-half cup of berries in each individual ramekin, or place all the berries in one baking dish. Add banana slices.
Sprinkle oat mixture evenly on top of banana and berries (about 2 Tablespoons per ramekin), then dot the tops evenly with butter and lightly spray top with cooking spray oil. Bake for 15 to 20 minutes until the topping is golden brown.