In a small bowl, combine the rolled oats, flax seeds, and sunflower seeds. Pour the boiling water over them, stir well, and let sit for at least 30 minutes, or up to several hours, until the water is fully absorbed and the mixture has cooled to room temperature.

In a large mixing bowl (or the bowl of a stand mixer), combine the warm water (105-115°F / 40-46°C), active dry yeast, and honey. Stir gently and let sit for 5-10 minutes until the mixture becomes foamy, indicating the yeast is active.

In a separate medium bowl, whisk together the all-purpose flour, whole wheat flour, rye flour, oat flour, and salt.

Add the flour mixture, olive oil, and the cooled soaker mixture to the yeast mixture. If using a stand mixer, attach the dough hook and mix on low speed for 2-3 minutes until a shaggy dough forms. If mixing by hand, stir with a sturdy wooden spoon until just combined.

If using a stand mixer, increase the speed to medium-low and knead for 8-10 minutes until the dough is smooth, elastic, and pulls away cleanly from the sides of the bowl. If kneading by hand, turn the dough out onto a lightly floured surface and knead for 10-15 minutes, adding small amounts of flour if the dough is too sticky, until it's smooth and elastic.

Lightly grease a clean large bowl with olive oil. Transfer the dough to the bowl, turning it once to coat all sides. Cover the bowl tightly with plastic wrap or a clean kitchen towel and let it rise in a warm, draft-free place for 60-90 minutes, or until it has doubled in size.

Gently deflate the risen dough by pressing it down. Turn the dough out onto a lightly floured surface. Shape it into a rectangular loaf by gently patting it into a rectangle (roughly 9x12 inches). Fold the longer sides of the rectangle into the center, overlapping slightly. Then, starting from one of the short ends, roll the dough up tightly into a log. Pinch the seam closed firmly.

Lightly grease a 9x5 inch loaf pan. Place the shaped dough into the prepared pan, seam-side down. Cover loosely with plastic wrap or a clean kitchen towel and let it rise in a warm place for another 45-60 minutes, or until it has nearly doubled in size and crowned slightly above the rim of the pan.

About 15 minutes before the end of the second rise, preheat your oven to 375°F (190°C). If you want a crispier crust, place a shallow oven-safe pan on the bottom rack of your oven.

Once the dough has risen sufficiently, gently brush the top of the loaf with a little water or milk and sprinkle evenly with the mixed seeds. If using a steam pan, carefully pour about 1/2 cup of hot water into it (this creates steam for a crispier crust). Immediately place the loaf pan in the preheated oven.

Bake for 35-40 minutes, or until the crust is deeply golden brown and the internal temperature of the bread reaches 190-200°F (88-93°C) when measured with an instant-read thermometer.

Remove the bread from the oven. Immediately turn it out of the loaf pan onto a wire cooling rack. Let it cool completely for at least 1-2 hours before slicing. Slicing warm bread can result in a gummy texture.