Place the oats, sunflower seeds, flax seeds, poppy seeds and brown sugar in a large bowl. Pour in the boiling water and stir to combine. Allow the bowl to sit for 15 to 20 minutes, until the temperature of the water has dropped to between 105° and 110°F. As the seeds absorb the water, they will plump up.
Stir in the yeast, sourdough discard, salt and olive oil. Add the all-purpose flour and combine well. Add 1½ cups of the whole wheat flour, ½ cup at a time, mixing well after each addition.
Form the dough into a ball and turn out onto a floured surface. If the dough is too sticky to work with, add 1 to 2 tablespoons more of the whole wheat flour or as needed. Knead for about 7 minutes, until smooth and elastic, adding more flour to the work surface as needed. Place in a greased bowl, turn the dough over to lightly grease the entire surface, and cover with a plate. Let rest for 1½ hours in a warm spot, until doubled in size.
Grease two 8- by 4-inch metal loaf pans. Punch down the dough. Turn it out onto a floured surface and cut the dough into two halves. Flatten the first half into an 8-inch square. Roll up the dough and push in the sides gently, until you have formed an even log. Repeat with the second half of the dough, place the formed loaves in the pans, seams down, and tuck the ends under the loaves.
Cover the loaves with a dishtowel. Let rest in a warm spot for about 1 hour, until they puff up to near the top edge of the pan.
About 15 minutes before the bread is ready to bake, preheat the oven to 425°F. Bake the loaves for 25 to 30 minutes or until browned on top and the bottom of the loaves sound hollow when you tap them. Remove the loaves from the pans and cool on a wire rack before slicing.
Store the loaves in clean cloth produce bags at room temperature for 2 days, or store, unsliced, in the freezer for up to 2 weeks.