Preheat your oven to 400°F (200°C).
Place the halved acorn squash on a baking sheet, cut sides facing up. Brush the cut sides with olive oil and season with a pinch of salt. Roast in the oven for about 40-45 minutes until the flesh is tender and edges are golden brown.
While the squash roasts, prepare your filling: in a mixing bowl, combine cooked grains, chopped vegetables, minced garlic, dried herbs, and a splash of olive oil. Season with salt and pepper to taste, and mix until well combined.
Once the squash is cool enough to handle, use a spoon to carefully scoop out a portion of the flesh, leaving a border intact to keep the shells sturdy. Mash the scooped flesh and fold it into the grain mixture for added flavor and moisture.
Fill each hollowed-out squash half with the grain and vegetable mixture, pressing gently to pack it in evenly. Sprinkle shredded cheese on top if using.
Return the stuffed squash to the oven and bake for an additional 10-15 minutes, until the filling is heated through and cheese (if added) is melted and bubbly.
Remove from the oven, let cool slightly, then serve warm. The squash should be tender with a slightly crispy top and a vibrant, hearty filling in every bite.