Combine warm water (like bath water, or 110 degrees F / 43 C), yeast, maple syrup (or other sweetener), salt, flaxseed meal, and flours in a large mixing bowl and stir. The result will be a sticky, rough dough. If using a stand mixer, beat at medium speed for about a minute. Otherwise just use a spoon to stir until well combined and when it can no longer do the job, knead and turn it in the bowl with your hands. Add flour until the dough is no longer sticking to the sides - about 3 3/4 cups total (amount as original recipe is written // adjust if altering batch size).
Lift the dough out and lightly grease the bowl with nonstick spray or olive oil. Cover and let rise for 2 hours at room temperature and 2 hours in the fridge. Alternatively, if you only have 2 hours, let rise at room temperature and skip the fridge (though a longer rise is best).
Use fingers to create a small hole in the dough and pour in sunflower seeds and oats. Transfer dough to a lightly floured work surface and knead about 20 turns or until elastic. Form into a loaf-like shape.
Place seam-side down in a lightly greased loaf pan or baking sheet and sift a light coating of flour over the top to help keep the dough moist. Loosely cover with plastic wrap and let rest for 45-60 minutes.
Preheat oven to 425 degrees F (218 C)* toward the end of the dough resting time and place a metal or cast iron pan (NOT glass, Pyrex, or ceramic) on the lowest oven rack. Also have 1 cup of hot water ready.
When the oven is preheated, slash the bread 2 or 3 times with a knife, making a cut about ½-inch deep.
Place in oven on middle rack. Then carefully pour hot water into the shallow pan on the rack beneath. Expect it to bubble and steam; then close oven door quickly.
Bake the bread for 26 to 35 minutes, or until deep golden brown and risen.
Remove the bread from the oven and let rest in the pan for 5 minutes. Then carefully remove from pan and transfer to a cooling rack to cool. Let it cool completely before slicing for best results (otherwise it can be doughy in the middle).
Store leftovers in a plastic bag at room temperature for up to a few days. Transfer to freezer for longer term storage.
*Based on some users' experience, I lowered the baking temperature to 425* F (from 450) to ensure the middle gets all the way done. I've had success at 450* F, but it seems some people's ovens or loaf pans are not allowing it to cook all the way through. This information was updated 3/15/16. *Adapted from my 7 Ingredient Muesli Bread. *Nutrition information is a rough estimate.