Preheat oven to 400 degrees. Spread squash on a parchment paper lined baking sheet. Drizzle with 1 tablespoon of olive oil. Bake for 10 minutes.
To create the dressing, add dijon mustard, maple syrup, sesame oil, and garlic to a small bowl. Stir to combine.
Add the asparagus and tomatoes to the baking sheet with the partially cooked squash. Drizzle the remaining tablespoon of olive oil and maple mustard dressing over everything. Season with salt and pepper. Stir so the vegetables are well coated.
Use a spatula to create four spaces for the halibut. Add the halibut to the baking sheet. Salt and pepper the top of the halibut. Bake the veggies and fish for 15 to 20 minutes or until halibut is cooked and squash is tender.