Preheat the oven to 400. Cut the squash in half, remove the seeds and place on a baking sheet. Fill each hole of the squash with water. Place in the oven for about 30-45 minutes until a spoon can easily cut into the flesh.
Once it is in the oven, cut half of the onions into quarter pieces and dice the other half of the onions finely. Chop up the carrots and celery stalks as well. Saute in a dry pot over medium-low heat for about 10-15 minutes until the carrots and celery are softened. Add a splash of water if the veggies start to stick to the pan. Add the broth and bring up to a simmer.
Meanwhile, peel off most of the skin of the ginger, not worrying to do every last crevice. In a dry skillet (avoid non-stick for this as it may start smoking) over high heat, place the quarter pieces of onions, peeled garlic cloves and the ginger broken into chunks into the skillet. Once the side touching the skillet receives a solid burnt mark, flip it over. Do every side that is possible. Keep a lid on the pan in between flipping the pieces to help them soften as well.
Once the squash is tender, cool it until you are able to easily peel it. Place the chunks of squash and the charred aromatics in a blender along with most of the soup. Blend up the soup in batches, or use an immersion blender instead if you prefer.
Place the blended soup back in the skillet and set over low heat. Season with salt and pepper, adding more to taste as needed. At the very end, just before serving, stir in the lime juice.
