Preheat oven to 400°F and line baking sheet with parchment paper. Set aside.
Rinse acorn squash of dirt and debris and pat dry.
Cut acorn squash in half (either way will work, whatever is easiest!).
Using a metal spoon, scoop out the "brains" of the squash, removing any seeds and gunk in the cavity.
Brush olive oil on the inside part of the acorn squash (both the edge and cavity). Sprinkle with salt and pepper, and lay cavity-side down on prepared baking sheet.
Bake for 35-45 minutes, or until squash is easily poked through with fork. The inside flesh of squash should be tender.
While the squash is roasting, start preparing the rice and vegetable medley.
In a pot of InstantPot, cook rice according to package instructions.
In a saucepan, add 1 tbsp olive oil over medium heat.
Add onion, garlic, celery, bell pepper, and 3 tbsp water. This will allow the vegetables saute without burning. Allow to saute for about 10 minutes, stirring occasionally.
Once onions have become translucent, add mushrooms, navy beans, fennel seed, fennel leaves, garlic salt, thyme, and 2 tbsp parsley (leaving some for garnish). Stir and allow to simmer for another 10 minutes.
When rice is done, add to vegetable medley. Stir well and remove from heat.
After squash is done roasting, allow to cool for 10 minutes.
Divide the rice and vegetable medley and spoon into the cavity of each acorn squash.
Garnish stuffed squash with parsley and pine nuts.
