Preheat oven to 180ºC. Lightly grease a 28×18×2.5-cm baking tin or a 20-cm square tin.
Place butter, oil, sugar, honey and orange rind and juice in a heavy-based saucepan. Heat gently, stirring until the butter has melted. Remove the pan from the heat and stir in the dates and walnuts. Add oats, stirring until they are evenly coated with the butter mixture.
Spoon mixture into the baking tin, pressing it down firmly and evenly. Sprinkle sunflower seeds on the top and press down so they are lightly embedded in the surface.
Bake for 20 minutes or until deep golden around the edges. Remove from the oven; leave in tin to cool slightly. Using a sharp knife, score the top into 16 equal pieces.
Leave to cool completely, still in the tin, before cutting into bars along the marked lines. Bars can be kept in an airtight container for up to 1 week.