In a small bowl, gently whisk together the warm water, yeast, and maple syrup. Let stand for 5 minutes, or until a foams develops on the surface.
Meanwhile, generously flour a clean work surface. Gather two large glass bowls (one for mixing and one for rising). Lightly grease one with olive oil and set aside.
Add the spelt flour to un-greased mixing bowl. Create a well in the center and add the yeast mixture, pumpkin puree, 1 tablespoon of the olive oil, and the sea salt. Use a large wooden spoon to stir and mix until all of the flour has been incorporated.
Turn the dough out onto the flour-dusted work surface. Knead for 2 to 3 minutes, until the dough is smooth and springy, adding plenty more spelt flour as needed (I usually add another ½ to 1 cup). You'll know it's ready when it begins to hold its shape and springs back, slightly but not completely, when pressed. The gluten in spelt is delicate, so be careful not to over knead or you'll end up with dry, crumbly focaccia.
Shape the dough into a ball and place it in the greased bowl. Cover the bowl with a clean kitchen towel and let the dough rise in a warm place for 1 hour, or until doubled in size.
When the dough has just a few minutes left to rise, line a large baking sheet with parchment paper.
Punch down the dough and turn it out onto a well floured surface. Knead it for just 15 seconds or so. Then, turn it out onto the lined baking sheet. Use your hands to gently form the dough into a rectangle that is approximately 6 by 12 inches in size. Use your pointer finger to poke holes in the dough.
Lightly brush the top of the dough with the remaining 2 tablespoons olive oil. Top with the red onion rounds and sprinkle with the rosemary and kosher salt.
Loosely cover the pan with parchment paper and let the focaccia rise for another 45 minutes, or until doubled in size. Meanwhile, preheat the oven to 350F.
Bake for 28 to 35 minutes, or until the bottom is golden brown and slightly crisp.