Preheat the oven to 375° F.
Rub the cut side of each squash half with olive oil, and oil an ovenproof dish or baking sheet. Sprinkle the whole baking dish with 1/2 teaspoon of the salt. Lay the squash, cut side down, in the dish and bake until it's very tender when pricked with a fork, 30 to 40 minutes. Remove the squash from the oven and increase the oven temperature to 425°F.
Meanwhile, heat the remaining olive oil in a large skillet over medium heat. Add the chorizo and fry until browned. Remove from the pan and set aside. Add the leeks to the hot oil and cook until soft, about 3 minutes. Add the apple, remaining 1/4 teaspoon salt, and pepper, and cook for another minute. Add the greens and cook until sorta wilted and softened, about 2 minutes. Add the sage, cooked grains, and reserved chorizo. Cook for another minute, stirring to combine, and remove from heat. Taste, and adjust the salt and pepper, if needed.
Turn the cooked squash over in the baking dish so it's cut side up. (Be careful as steam will escape when you turn the squash.) Scoop the filling into the cavity of each squash half, piling it into a mountain so that it holds as much as possible. If desired, sprinkle with the cheese. Bake until everything is warmed through, about 15 minutes. Serve warm.