Preheat the oven to 200°C.
Place all the ingredients in a large bowl. Add the boiling water. Give it a stir and let sit 20 minutes.
Grease a rectangular cake or loaf pan and line it with parchment paper.
Use a spatula to put the oat and seed mixture in the loaf pan. Press it down tightly.
Bake for 70 minutes at 200°C.
Let cool completely before slicing.