Preheat oven to 400°F (200°C).
Brush the cut sides of the acorn squash with 1 tablespoon of olive oil and season with salt and pepper.
Place squash cut-side down on a parchment-lined baking sheet and roast for 35-40 minutes until tender.
While squash roasts, heat the remaining olive oil in a skillet over medium heat.
Sauté onion, celery, and carrots for 5-7 minutes until softened.
Add garlic and thyme, cooking for 1 minute until fragrant.
Stir in the cooked rice, cranberries, pecans, and vegetable broth.
Simmer the mixture for 3-5 minutes until the broth is absorbed.
Flip the roasted squash halves and fill the cavities with the rice mixture.
Return to the oven for 10 minutes to heat through and lightly brown the tops.