Preheat the oven to 180 degrees C. Grease a 900g loaf tin and line with baking paper.
In a large mixing bowl combine the flour, sugar, oats and seeds (if using) then mix well.
In a separate bowl whisk the eggs lightly then add the juice and zest of the oranges. Beat in the butter and a splash of milk. Gradually add the wet ingredients to the dry and mix until well incorporated. Pour into the prepared loaf tin.
Bake in the preheated oven for 40 to 50 minutes until a skewer inserted into the centre of the cake comes out clean. Remove from the oven and allow to cool on a rack before slicing and enjoying.