Make the dough: In a large ungreased mixing bowl, whisk the flour and yeast together. Add the oats, pumpkin seeds, sunflower seeds, flax seeds, and salt and whisk to combine. Mix the honey and water together, and then pour over the dry ingredients. Using a rubber spatula or wooden spoon, gently mix together. The dough will seem dry and shaggy, but keep working it until all the flour is moistened. The dough will be sticky. Shape into a ball in the bowl as best you can.
Keeping the dough in the bowl, cover the dough tightly with plastic wrap or aluminum foil and set on the counter at room temperature. Allow to rise for 3 hours. The dough will mostly expand out, stick to the sides of the bowl, and have a lot of air bubbles.
Place covered dough in the refrigerator for 12 hours to 3 days. (Note: You can continue with step 5 immediately, but for the absolute best flavor and texture, I strongly recommend letting this risen dough rest in the refrigerator for at least 12 hours and up to 3 days. )
Lightly dust a large nonstick baking sheet with a little flour and/or cornmeal. Using generously floured hands and gentle pressure so as to not deflate the dough too much, shape the risen dough into a ball. Dough is very sticky.
Transfer ball to prepared baking sheet. Mix topping ingredients together. Sprinkle on top of dough, and if the seeds aren't sticking, press them into the dough as best you can. Loosely cover and allow dough to rest for 45 minutes. You will bake the dough on this prepared baking sheet. (See notes below for instructions to bake in a Dutch oven.)
During this 45 minutes, preheat the oven to 425°F (218°C).
When ready to bake, using a very sharp knife or bread lame, score the dough with a slash or X about 1/2 inch deep. If the shaped loaf flattened out during the 45 minutes, gently use floured hands to reshape.
Optional for a slightly crispier crust: After the oven is preheated and bread is scored, place a shallow metal or cast iron baking pan or skillet (I usually use a metal 9x13-inch baking pan) on the bottom oven rack. Carefully and quickly pour 3–4 cups of boiling water into the shallow pan. Place the scored dough/baking pan on the center rack. Quickly shut the oven to trap as much steam inside. The steam helps create a crispier crust.
Place the shaped and scored dough (on the flour/cornmeal-dusted pan) in the preheated oven on the center rack. Bake for 40 minutes or until the crust is golden brown and an instant read thermometer reads the center of the loaf as 195°F (90°C). If you noticing the exterior browning too quickly, tent the bread with aluminum foil.
Remove the bread from the oven and allow to cool for at least 10–20 minutes before slicing and serving.