Preheat the oven to 400°F
Wash the acorn squash well, and cut it lengthwise (from top to bottom)
In a small bowl, mix 2 Tbsp of olive oil with 3 garlic cloves, onion powder, and salt and pepper to taste
Using a fork, pierce the inside part of both acorn squash halves.
With a basting brush, brush the olive oil mix all over the inside and outside of the squash halves
Roast for 40-60 minutes, or until squash is fully cooked and tender
While the squash is roasting, prepare the stuffing. On medium heat, boil together the vegetable broth, rosemary sprigs and wild rice.
Once boiling, set heat to low, cover the pot and simmer for around 30 minutes, or until most of the liquid has evaporated and the rice is cooked
Heat 2 Tbsp of olive oil in a pan on medium heat, and saute the mushrooms. Be careful not to crowd them, keeping them in a single layer. Saute one side during 1 minute, flip, and cook for 2-3 minutes more, until nicely browned. Remove from heat and place in a separate bowl
In the same pan, saute the onion and celery until tender, around 5 minutes. Add the garlic and cook until fragrant, around 1 minute
Remove from heat and add the vegetables to the bowl with the mushrooms. Add the thyme, salt and pepper and mix well
Once the wild rice is ready, remove the rosemary stems (leave the leaves) and add it to the vegetables in the bowl. Combine well
As soon as the acorn squash is fully cooked, stuff each half with the wild rice and vegetable stuffing. Sprinkle with sliced almonds and decorate with rosemary sprigs