Preheat the oven to 350 degrees. Use a fork to stab holes all over the squash. Place onto a baking sheet and into the oven for 1 hour or until soft.
Meanwhile heat 2 Tbsp. oil in a large pot over a high flame until hot. Add the onions, carrots and celery, and season with a pinch of salt. Cook for about 10 minutes, stirring occasionally. Add the mushrooms and season with a pinch of salt. Cook until wilted and slightly browned, about 12 minutes. Add the garlic and stir to combine. Continue cooking another 3 minutes. Add the tomato sauce and a pinch of salt. Bring to a simmer and reduce heat to low. Stir often, cooking until the sauce thickens and resembles hot cereal, about 30 minutes.
Cut the squash in half and scoop out the seeds. Scrape the inside flesh with a fork to resemble spaghetti. Divide between 2 plates and top with the mushroom bolognese.