Preheat oven to 400°F and line a baking sheet with parchment paper.
Cut the butternut squash in half lengthwise and scoop out the seeds. Brush with 1 tbsp olive oil and place cut-side down on the baking sheet. Roast for 40 minutes or until fork tender.
While the squash roasts, combine the steel cut oats and vegetable broth in saucepan. Bring to a boil, reduce heat, and simmer for 20-25 minutes until tender.
Heat the remaining 1 tbsp olive oil in a large skillet over medium heat. Add the onion and mushrroms and cook for 5-7 minutes until softened.
Stir in the rosemary, chickpeas, spinach, garlic, walnuts and Dijon mustard. Cook for 2-3 minutes until the spinach wilts.
Transfer the cooked oats to a large bowl. Add the vegetable and chickpea mixture, cranberries, and lemon juice. Stir to combine.
Once the squash is cool enough to handle, sccop out a small amount of the flesh, leaving about a 1/2 inch border. Reserve the squash flesh for soups, smoothies, or another recipe.
Fill each sqaush generously with oat mixture.
Drizzle with balsamic glaze and garnish with fresh rosemary before serving.