In a large bowl, place flours, oats, sunflower seeds, brown sugar, salt, sesame seeds, flax seeds, yeast, and fennel seeds. Add 13⁄4 cups plus 21⁄2 tablespoons (432 grams) warm water, and stir by hand until fully incorporated and a sticky dough forms. (Alternatively, place flours, oats, sunflower seeds, brown sugar, salt, sesame seeds, flax seeds, yeast, and fennel seeds in the bowl of a stand mixer fitted with the paddle attachment. Add 13⁄4 cups plus 21⁄2 tablespoons [432 grams] warm water, and beat at medium speed until a sticky dough forms, about 30 seconds.)

Cover and let rise in a warm, draft-free place (75°F/24°C) for 2 hours. Then, refrigerate for at least 2 hours (preferably overnight).

Turn out dough onto a lightly floured surface, and gently press dough just to level and even it out.
Starting on left side and working clockwise, fold edges of dough toward center, pressing lightly. Turn dough ball over, and using both hands, cup dough, and pull it toward you. Turn dough 909 degrees, and repeat until you have a smooth, tight, sealed round.
Dust a sheet of parchment paper with rye flour; place dough on parchment, seam side up. Cover and let rise in a warm, draft-free place (75°F/24°C) for 1 hour.
When dough has 30 minutes left to rise, place a 6- to 7-quart Dutch oven and lid in a cold oven. Preheat oven to 500°F (260°C).

Mix multi-seed topping ingredients.

Carefully remove hot Dutch oven from oven; remove lid, and quickly turn bread into Dutch oven so seam is now on bottom. Brush top of loaf with water, and sprinkle with Multi- Seed Topping. Score top of bread (being careful not to touch hot sides of Dutch oven). Cover with lid, and place back in oven.
Immediately reduce oven temperature to 450°F (230°C). Bake for 25 minutes. Remove lid, and bake until an instant-read thermometer inserted in center registers 190°F (88°C), about 15 minutes more.
Immediately remove loaf from Dutch oven, and let cool completely on a wire rack.