In the baking dish spread out the walnuts and toast for 5minutes or until the nuts start to get a little brown. Remove and set aside to cool.
While the nuts are cooling, using a whisk, mix the brown sugar, flour, salt, cinnamon, oats, and baking powder together. Once the nuts have cooled use a food processor or knife to roughly chop them and add to the mixture. Pour in the melted butter and use a spatula to combine.
Line the baking dish with parchment and pour about ⅔ of the mixture into the dish and press down so it is evenly spread and compact. Pour the jam over the granola and spread gently and evenly with the spatula. Some of the granola might get mixed in but that is ok. Add the rest of the granola and gently pack so there is no loose granola. Don't push so hard the jam leaks out.
Bake for 40 minutes and remove from the oven to let cool completely before slicing.