Preheat oven to 375°F. Generously grease an 8 x 8-inch pan.
In medium bowl, combine melted butter and 1 teaspoon vanilla. Stir in flour, oats, sugar, xanthan gum, baking powder, lemon zest and salt until thoroughly blended.
Press 1 cup oat mixture firmly into bottom of the prepared pan. Stir remaining teaspoon of vanilla into raspberry jam until smooth, then spread evenly on top.
Sprinkle remaining oat mixture over jam, then pat firmly to make top layer smooth and even.
Bake 20-25 minutes, or until top is lightly browned and firm. Cool bars in pan for 30 minutes on wire rack. Cut into 16 squares and serve at room temperature.
