Place the uncut acorn squash in the oven directly on the center rack. Turn on the oven to preheat to 400° F. Allow the squash to remain in the oven while it heats up. Once the oven reaches 400°, carefully remove the squash using oven mitts. Allow the squash to rest until they are cool enough to handle. Then slice each squash in half lengthwise and scoop out the seeds. Discard the seeds (or save for roasting later.)
Place the squash on a baking sheet (line with parchment paper for easier cleanup) cut side down. Bake the squash for 40 minutes until the squash are nearly tender when pierced with a fork. Remove the baking sheet from the oven. Carefully turn the squash halves over so they are cup side up.
Meanwhile, prepare the quinoa. First rinse the quinoa with cold water in a fine mesh strainer. Add the quinoa and 1 cup of water to a small saucepan. Bring to a boil. Then reduce the heat and cover and simmer for 15 to 20 minutes until the water has been absorbed.Or to prepare in an Instant Pot pressure cooker, place the rinsed quinoa and ½ cup plus 2 tablespoons water in the liner. Close and lock the lid. Cook on high pressure for 5 minutes. Allow the pressure to release naturally.Set aside the cooked quinoa.
Heat the oil in a large skillet over medium heat.
Add the onion and saute until soft and slightly translucent.
Add the carrots and celery and saute until soft.
Then add the garlic and saute for about 30 seconds until fragrant.
Next add the cooked quinoa, chickpeas, tomatoes, lemon juice, and thyme and stir to combine.
Cook until all the ingredients are heated through and the tomatoes are soft, stirring occasionally.
Taste and add salt and pepper, as needed.
Spoon the quinoa mixture into the squash halves. Bake for 10 to 15 minutes or until the squash are tender.
The quinoa can be cooked in advance. ½ cup quinoa will yield about 1½ cup cooked.To prepare the filling in advance, refrigerate the cooked and cooled mixture for up to 3 days. Leftover stuffed squash can be refrigerated and reheated in the oven or microwave. Or enjoy at room temperature.