Combine the milk and vinegar in a small bowl and stir to combine. Mix in the oats. Cover and refrigerate overnight.
Remove the oats from the refrigerator. In a large bowl, combine the buckwheat flour, hemp hearts, flaxseed meal, psyllium, chia seeds and salt and stir to combine. Mix in the pumpkin seeds, sunflower seeds, almonds and walnuts.
In a 2-cup glass measuring cup, combine 1 cup hot water and the maple syrup. Let cool (or heat in the microwave) to 100-110℉. Sprinkle the yeast over and mix in. Let stand until the mixture begins to foam and smells delightfully yeasty. Add to the dry ingredients. Add the oat mixture and olive oil and mix very well. The dough will seem thin at first, but will thicken as you stir it.
Cover the bowl with plastic wrap and let the dough rise in a warm area until slightly puffy and feels less dense (it will not rise as high as other breads), 1¼-1½ hours.
Line an 8x5" glass loaf pan with parchment paper. Stir the dough to deflate. Spoon into the loaf pan, smoothing the surface a little. Cover with plastic wrap and let rise in a warm area until puffy and slightly domed, 1-1¼ hours.
Preheat the oven to 350℉. Remove the plastic wrap and bake the bread until it is dark brown, firm to the touch an an instant-read thermometer inserted into the center registers 190-200℉, about 1 hour 20 minutes.
Transfer the pan to a rack and let the bread cool for 10 minutes. Turn the bread out onto the rack, remove the parchment and cool completely before slicing (unless, like me, you can't resist cutting off an end, spreading it with butter and tasting your creation warm). Let stand on the rack over night before wrapping airtight. Store in the refrigerator or up to 2 weeks, or slice and freeze.