Mix the starter, water, honey, and oil, in a large bowl, with a dough whisk or fork. Add the flours and salt to this. Mix the dough by hand in the bowl to form a shaggy dough. Cover with a damp towel or plastic wrap and allow to rest for 30 minutes.
While the dough is resting, mix your choice of grains and seeds, and hot water in a separate bowl. Let it sit for about 30 minutes. Drain the water thoroughly before using.
Add the soaked and drained multigrains to the dough and knead to incorporate. The dough will be wet at first but will begin to come together. Do not add more flour or the texture of the bread will suffer.
Cover the bowl with plastic wrap or a damp towel and let rise until doubled, about 5 to 8 hours, depending on your ambient temperature. I prefer to mix the dough at night and let it rise overnight in the fridge. I take the dough out first thing in the morning and let it come to room temperature before I proceed.
Place the dough onto a lightly oiled surface and press it out to a rectangle. One side of the rectangle should be about 9 inched to fit into your loaf tin. Roll the dough into a log and place it into an oiled 9 inch by 5 inch loaf tin, seam side down. Cover loosely with oiled plastic wrap and let rest until the dough has risen upto one inch above the rim of the pan. This should take about 1 to 2 hours.
If using oats (and/or seeds), brush the top of the loaf with water and lightly press them in.
Pre-heat your oven to 230C (450F). Place the loaf tin in the oven on the centre rack the center rack. Reduce the temperature to 200C (400F) and bake for 50 to 60 minutes until done. Cool in the pan for 10 minutes and then turn it out to a wire rack to cool completely. Do not slice until the bread has cooled down well. You will be able to slice quite thin slices.