HEAT oven to 325 degrees F. Toss together in a large mixing bowl oats, flour, brown sugar, walnuts, cinnamon, nutmeg, lemon peel and salt until well blended.
SPRINKLE mixture with lemon juice, then with a pastry blender or two knives, cut in the butter pieces until mixture is crumbly.
SPRAY 13 x 9-inch baking pan with no-stick cooking spray. Reserve 2 cups of the oat mixture, then sprinkle remainder in pan, pressing with fingers to form a crust
BAKE 10 minutes, or until set. Let cool slightly, then spread blackberry jam evenly over crust. Sprinkle evenly with reserved oat mixture, pressing down gently.
RETURN to oven; bake 15 to 20 minutes, or until crust is golden brown.
*To toast nuts: Place walnuts in dry nonstick skillet; cook over medium heat, shaking pan until nuts are lightly browned.