Who says stuffing has to be bread-based? Here, wheatberries and millet are dressed up with two types of mushrooms, Middle Eastern spices, and for a pop of sweetness, golden raisins. It's used both to fill Roasted Acorn Squash for a hearty vegetarian main dish and to accompany Roasted Turkey Rubbed with Coriander, Black Pepper, and Fennel.
Soak wheatberries in cold water overnight in the refrigerator (or place in a pot, cover with water by 1 inch, and bring to a boil; then remove from heat and let stand 1 hour). Drain; set aside.
Heat oil in a large straight-sided skillet over high. Add onion, garlic, 2 teaspoons salt, and 1/2 teaspoon pepper and cook, stirring occasionally, until onion is translucent and golden around the edges, 5 to 6 minutes. Add cumin and coriander and cook until fragrant, about 30 seconds. Add mushrooms and cook, stirring, until liquid evaporates and mushrooms begin to brown, 7 to 9 minutes. Add wheatberries; toss to coat.
Add broth, 1 cup water, and saffron; bring to a boil. Cover, reduce heat, and simmer until wheatberries are tender but retain some bite, about 1 hour. Stir in millet (if pan seems dry, add 1/2 cup water) and cook, covered, until grains are tender, 30 to 40 minutes. Remove from heat. Stir in raisins, lemon and orange zests and juices, and parsley; season with salt and pepper. Stuffing can be made ahead and refrigerated in an airtight container up to 3 days.