Preheat the oven to 200 degrees. Cook the quinoa in plenty of salted water for twelve minutes until just tender, drain, and let it steam dry. It will continue to cook slightly in the oven, so deliberately leave it a little al dente.
Halve the bell peppers lengthwise and remove the seeds and membranes, but leave the stem intact so the halves keep their shape. Rub them with a tablespoon of olive oil and some salt, and place them in the oven for ten minutes, hollow side down. This softens them without the filling drying out later.
Meanwhile, finely chop the onion and mince the garlic. Heat a tablespoon of olive oil in a frying pan and sauté the onion over medium heat for six minutes until translucent. Add the garlic, oregano, and paprika powder and cook for another minute. Stir in the spinach until wilted, then squeeze out any excess moisture.
Toast the pine nuts in a dry pan until golden brown. Mix the quinoa with the spinach mixture, half of the crumbled feta, some lemon zest, salt, and pepper. Turn the bell peppers over, fill them generously, and crumble the remaining feta on top. Bake for another twenty minutes until the top is golden brown. Finish with the pine nuts, parsley, and the remaining olive oil.