Choose a smaller squash for a family meal, or a giant squash and serve on a platter at a dinner party.
Preheat the oven to 400 degrees F. Trim off the limes' tops and bases using a small sharp knife. Stand each lime on a chopping board and cut down the sides of the fruit, following its natural curves, to remove the skin and white pith. Quarter the limes from top to bottom, and cut each quarter into thin slices, about ⅛ inch thick. Place them in a small bowl, sprinkle with a little salt, drizzle with 1 tablespoon of the olive oil, stir and set aside.
Next, cut the squash in half lengthways, scoop out the seeds and discard. Cut each half, top to bottom, into ⅜-inch-thick slices and lay them out on a large baking sheet lined with parchment paper.
Place the cardamom pods in a mortar and work with a pestle to get the seeds out of the pods. Discard the pods and work the seeds to a rough powder. (Note, I used ground cardamom). Transfer to a small bowl;, add the allspice and the remaining 3 tablespoons of oil, stir well and brush this mixture over the butternut slices. Sprinkle over a little salt and place in the oven for 15 minutes or until tender when tested with the point of a knife. Remove from the oven and set aside to cool. Peel off the skin, or leave on if you prefer (or peel before baking).
Meanwhile, whisk together the yogurt, tahini, lime juice, 2 tablespoons of water and a pinch of salt. The sauce should be thick but runny enough to pour; add more water if necessary.