1) Preheat the oven to 180C/Gas 4.
2) Brush the cut side of each acorn squash with the butter and sprinkle with salt and pepper. Place squash, cut-side down, on a baking sheet and bake until almost tender, about 30 mins.
3) While the squash is baking, combine the orange juice, brown sugar, allspice, and cinnamon in a medium saucepan. Cook over high heat until reduced to 240ml, stirring often.
4) Preheat the griddle to medium-high. Place the squash, cut side up, on the griddle, and brush with the orange glaze. Cook for 5 mins, turn over with tongs, and cook for 5 more mins or until tender and glaze is caramelised. Remove from the griddle and brush with more of the glaze. Serve warm.