Preheat oven to 350°F. Line a 9-by-13-inch pan with a large piece of foil; butter the foil.
In a large bowl with electric mixer on medium speed, combine flour, oats, both sugars, baking soda, salt and nuts. With mixer on low speed, add butter pieces. Beat for about 2 minutes, until blended.
Press about 2/3 of mixture evenly into the prepared pan. Bake for 20 minutes, until just golden.
Remove pan from oven, spread jam evenly over hot crust. Sprinkle remaining oat mixture evenly over jam.
Bake for 25 minutes, until jam bubbles and top is golden brown.
Transfer to a wire rack to cool.