Soak the wheat berries overnight in water. The next day, rinse the wheat berries and place in a saucepot. Place 2 cups of water in the pot and bring to a boil. Reduce heat to a simmer and cook until the wheat berries are chewy but not tough, about 30 to 35 minutes. Strain and set aside.
Place the wild rice in a separate saucepot and add 1 ½ cups water. Bring to a boil then reduce to a simmer. Let rice simmer until it begins to “pop”, about 35 to 40 minutes. Add additional water if needed. Strain and set aside.
Place the olive oil in a sauté pan and heat on medium. Add the white onion, garlic and celery and sauté for 2 to 3 minutes or until onion is translucent.
Transfer the sautéed vegetables to a mixing bowl. Add the cooked wild rice, cooked wheat berries, nuts, steamed sweet potato, dried fruit, 2 teaspoons maple syrup or honey, salt, thyme and pinch of pepper.
Preheat oven to 375 degrees. Place the acorn squash halves, cut side up, on a baking pan. Brush the squash halves with the melted butter and divide the brown sugar between the halves. Bake until the squash halves are just tender when poked with a paring knife tip. They will be baked again so be careful not to over bake them.
Remove from the oven but keep them on the baking sheet pan. Divide the grain mixture among the four squash halves. Place back in the oven and roast for another 15 to 20 minutes to heat through and finish roasting the squash.