Cut each squash in half and scoop out the seeds with a spoon. Drizzle 1/2 tablespoon olive oil over the cut side and season with kosher salt and fresh ground pepper. Place the halves cut side down on a baking sheet, and roast for about 35 minutes, until slightly browned and easily pierced with a fork. (The time will be less for smaller squashes.)
Cook the quinoa following the instructions found at Master Recipe: Perfect Quinoa, using 1 1/2 cups quinoa and 2 1/4 cups water. Or, use our Instant Pot quinoa method. While the quinoa cooks, complete Step 2 and 3.
Chop the leeks (watch the video!): Chop off the dark green stems of the leeks, then slice them in half length-wise. Place each leek half cut-side down on the cutting board, then chop it into thin half-moon shapes. Rinse thoroughly in a colander to remove any dirt. Remove the leaves of the thyme, and chop the sage leaves.
If not already chopped, roughly chop the walnuts.
In a skillet, heat 1 1/2 tablespoons olive oil. Add the leeks and sauté about 4 minutes, just before they begin to brown.
In a small skillet, toast the walnuts over low heat, until slightly browned, watching so they don’t burn.
When the quinoa is done, stir in the sauteed leeks. Then add the fresh sage, thyme, 1/2 teaspoon kosher salt, and fresh ground pepper. Taste, and add more salt or pepper to taste, and a drizzle of olive oil.
When the squash are done, spoon quinoa generously into each half. Top with walnuts and serve immediately.