Preheat oven 375F line baking sheet with parchment paper. Season squash with oil, salt and pepper. Place on baking sheet cut side up and roast for 35 to 40 minutes until squash has softened. Gently scoop up softened squash ensuring you leave squash cups in tacked for stuffing.
To make rice, in a large sauce pan, heat oil over medium heat.
Add onions and sauté for 5-6 minutes until soften and golden.
Stir in roasted squash, spinach and add vegetable stock.
Bring to a boil and add rice. Reduce heat to low, cover & cook for 12-15
minutes until liquid has been reduced but still slightly creamy.
Turn off heat, remove lid and cover top of pan with a tea towel. Place lid back on top of tea towel and let stand for 5-7 minutes for rice to slightly cool.
Fluff with fork and season with salt and pepper. Divide rice amongst squash halves and top each with a tbsp of feta. place in oven on broil and bake for a few minutes until feta has slightly melted. Garnish with Pine nuts or nuts of your choice if using.