Preheat oven to 200°C (390°F). Scoop a bit of the eggplant flesh out to create room for filling. Lightly score and brush both halves with olive oil and a pinch of salt. Roast face up on a tray for ~30 minutes or until tender.
While the eggplant roasts, rinse and cook quinoa in water or vegetable broth (1:2 ratio) for 15 minutes. Fluff and set aside.
In a pan, sauté onion, garlic, bell pepper, and zucchini in a little olive oil for 5–7 minutes until soft.
Stir in cooked quinoa, walnuts, lemon juice, herbs, salt, and pepper. Mix well.
Remove eggplants from the oven. Fill each half with the quinoa mixture. Return to the oven for an additional 10 minutes.
Serve warm, optionally topped with a bit of crumbled feta