Preheat oven to 325°F. Coat a foil-lined springform pan with canola cooking spray, or coat a 9-inch, deep-dish pie pan with canola cooking spray.
Add apple slices, cinnamon, and nutmeg to a large bowl and toss to blend. Pour apple mixture into prepared baking dish, arranging apple slices so they lay as flat as possible over each other.
In mixing bowl, beat sugar blend, milk, 1/2 cup biscuit mix, egg, egg substitute, and canola oil together on medium speed until smooth. Pour batter over apples.
Add remaining ingredients (1 cup biscuit mix, walnuts, brown sugar and margarine) to a 4-cup measure and mix with fork until crumbly. Sprinkle crumb mixture over the top of tart. Bake for 55-60 minutes, until knife inserted in the center comes out clean. Serve hot or cold.