This salad isn't just delicious, with its flavors of sweet squash, walnut, and pickled onions--it's economical, too. While the squash is roasting, whisk together vinegar, sugar, and salt and quickly pickle some sliced red onion for 15 minutes. When that's done, the pickling liquid becomes the base of the vinaigrette.
1-1/2 pounds kabocha squash, stem and seeds removed, skin on (see "Note," above), and cut into 1-inch-thick wedges
2 tablespoons plus 1/2 cup extra-virgin olive oil, divided
1-1/2 teaspoons table salt, divided
Freshly ground black pepper, to taste
1/2 cup rice vinegar
1/2 teaspoon granulated sugar
1/2 small red onion, peeled and cut into 1/4-inch-thick wedges
8 ounces baby spinach leaves, about 5-6 cups
1/2 cup walnut halves, roughly chopped
Preheat oven to 400°. Brush squash wedges with 2 tablespoons olive oil and sprinkle all over with 1 teaspoon salt plus ground pepper to taste. Line a baking sheet with aluminum foil and arrange squash slices on it. Roast until tender, 20-25 minutes.
Meanwhile, in a medium-size bowl, whisk together rice vinegar, sugar, and remaining 1/2 teaspoon salt. Add onion to vinegar and let sit at least 15 minutes (up to overnight). Put spinach leaves in a salad bowl and set aside.
In a small heavy-bottomed skillet, toast walnuts over medium-low heat until fragrant and golden brown, about 10 minutes. Remove from heat and cool; then add to salad bowl.
When squash is tender and cool enough to handle, cut into 1-inch chunks and add to salad bowl. Remove onions from vinegar mixture with a slotted spoon, reserving vinegar mixture, and add to bowl.
In a small bowl, whisk together vinegar mixture and remaining 1/2 cup olive oil. Pour one-third of the dressing over the salad and toss to coat lightly. Serve salad with extra dressing on the side.
Note: The skin of the kabocha squash becomes very tender with roasting, so there's no need to peel it if you don't want to.