Preheat the oven to 400º.

Brush the cut side of the squash with oil, and season with salt and pepper to taste.

Lay the squash, cut side down, on a parchment-lined sheet tray. Roast until the flesh is completely tender, about 45 minutes. Allow to cool a bit.

Using a fork, scrape the "meat" of the squash, so you have long spaghetti-like strands. Transfer to a bowl, and season with the cilantro, chili powder and lime juice to taste. Season with additional salt and pepper, if needed.

Spoon the squash back into the empty squash skins, and place in a baking dish.

Heat a sauté pan over medium heat, and add the grapeseed oil. Gently sauté the onions until softened. Add the cumin, and cook for an additional 30 second to 1 minute or until aromatic.  

Stir in the black beans, corn, tomatoes and jalapeño, and season with salt and pepper to taste. Spoon the mixture on top of the spaghetti squash, and top with the cheese. 

Bake for 5 minutes, or just until the cheese has melted.  

While the bowls are baking, prepare the guacamole. Remove the meat from the avocado and place in a bowl. Add lime juice, salt and pepper to taste. Mash this mixture with either a fork or potato masher until smooth, and stir in the cilantro.   

Top each bowl with a dollop of the guacamole, and finish with a sprinkling of crushed tortilla chips.