Add the avocado oil. Add the bison and cook until nicely browned on all sides - about 10 minutes.
Add the olive oil, carrot, onion, celery and garlic, and cook until fragrant - about 5 minutes.
Season to taste with salt and pepper. Add the red wine, beef stock, tomato paste, chopped tomatoes, oregano, and bay leaf.
Stir. Cover and reduce the heat to low. Simmer on low heat for 1 hour and 30 minutes, until the bison is tender. Meanwhile, preheat oven to 400° Fahrenheit.
Using a sharp knife, carefully slice the squash into 1.5 inch thick rings. Remove the seeds and place on a parchment lined baking sheet. If grilling, put them on a plate to bring out to the grill. Spray with avocado oil spray, and season with salt and pepper to taste.
Roast for 30 minutes per side in the oven, or grill them over direct heat for 15-20 minutes per side. To serve: spoon the bolognese into the centre of the squash rings. Top with the cheese, and broil until the cheese melts. Garnish with fresh basil.