Preheat your oven to 400°F (200°C). Place the halved squash on a baking sheet, cut side up, and brush with a little olive oil. Roast for about 30-40 minutes, or until the flesh is soft and caramelized around the edges, and the skin is starting to brown.
While the squash roasts, prepare the filling by combining cooked grains, drained beans, sautéed mushrooms, chopped spinach, sun-dried tomatoes, toasted nuts, olive oil, lemon juice, and a pinch of salt and pepper in a mixing bowl. Mix everything until well incorporated and the mixture feels cohesive but still slightly chunky.
Once the squash is tender and cool enough to handle, carefully scoop out most of the flesh into a bowl, leaving a small border to keep the shell intact. Mash the flesh slightly and fold it into the prepared filling to add moisture and flavor.
Taste the filling and adjust seasoning with more salt, pepper, or lemon juice if needed. The mixture should be flavorful and slightly moist but not runny.
Spoon the filling back into the roasted squash halves, pressing gently to pack it in evenly. Distribute any remaining filling among the halves if desired.
Return the stuffed squash to the oven and bake for another 10-15 minutes, until the filling is heated through and slightly bubbling, and the tops are golden.
Remove from the oven, let rest for 5 minutes, then sprinkle with fresh herbs for a burst of color and freshness.
Drizzle with extra olive oil or squeeze fresh lemon over the top for added brightness. Slice into wedges and serve warm to enjoy the crispy edges and flavorful filling.
