Preheat your oven to 200°C (390°F). Halve the squash lengthwise and scoop out the seeds and stringy bits with a spoon. Brush the insides lightly with 1 tablespoon of olive oil, then place cut-side down on a parchment-lined baking sheet. Roast for 40-45 minutes until the flesh is soft and caramelized around the edges.
While the squash roasts, cook the quinoa according to package instructions—usually boiling in twice the amount of water until fluffy and tender, about 15 minutes. Fluff with a fork and set aside.
Heat the large skillet over medium heat and add 1 tablespoon of olive oil. Sauté the chopped onion and minced garlic until fragrant and translucent, about 2 minutes. Stir in the cooked quinoa, drained black beans, chopped herbs, smoked paprika, cumin, salt, and pepper. Cook for another 3-4 minutes, until heated through and aromatic.
Once the squash is tender and cool enough to handle, flip them over carefully. Use a spoon to scoop out some of the flesh into a bowl, leaving about a 1/2-inch border to maintain the shell's shape. Mix this flesh into the skillet filling for extra moisture and flavor.
Gently stuff each squash half with the filling, pressing lightly to pack it in. Mound any extra filling on top if desired, then place the stuffed halves back onto the baking sheet.
Bake the stuffed squash for an additional 15-20 minutes at 180°C (356°F) until the filling is bubbling and the edges of the squash are caramelized and tender. Toast the chopped nuts in a dry skillet until golden and fragrant, about 2-3 minutes, then sprinkle on top of the baked squash.
Remove from the oven and let sit for 5 minutes. Drizzle with lemon juice or zest if using, and sprinkle with toasted nuts and extra herbs for color and flavor. Serve warm, directly in the squash shells for a beautiful presentation.
