Combine oats, birch syrup, butter and salt in a large bowl. Pour boiling water over top, stir and let sit until the mixture cools to room temperature, about 30 minutes.

Sprinkle yeast over 1/4 cup warm water. When the yeast has fully dissolved, usually about 5 minutes, stir yeast and water into the cooled oat mixture.

Stir in barley flour and walnuts. When thoroughly combined, stir in all-purpose flour until you have a stiff but still sticky dough (you might not need all the flour). Dust a counter with flour, transfer dough to the counter and knead for 7 to 10 minutes, using more flour, as necessary, to keep dough from sticking.

Form dough into a round, coat with 1 tsp of olive oil and transfer to a clean bowl. Cover bowl with a tea towel and allow dough to rise until doubled in size, about 1 hour.

Cut dough in half with a bench scraper or a sharp knife. Dust the counter and a rolling pin lightly with flour. Working with one piece at a time, roll dough into a rectangle, 8-inches wide and 12-inches long. Starting from the short side, roll the dough tightly into a log and pinch the ends and seam shut. Place seam-side down in a parchment-paper-lined loaf pan and repeat with the other half of the dough.

Cover loaf pans with a tea towel and allow loaves to rise until doubled in size, about 30 minutes. Preheat oven to 375℉. Place loaves on the middle rack and bake for 35 to 40 minutes, until tops are golden brown and a tester inserted in the middle of the loaf comes out clean.

Remove the loaves from the pans and cool on a rack, to room temperature, before slicing.