01 - Preheat oven to 400°F (200°C). Lightly grease a baking dish just large enough to hold the peppers upright.
02 - Place the quinoa and vegetable broth in a medium saucepan. Bring to a boil, reduce heat to low, cover, and simmer for 12 minutes or until quinoa is fluffy and water is absorbed. Remove from heat and let sit, covered, for 5 minutes.
03 - While the quinoa cooks, prepare the vegetables and herbs.
04 - In a large bowl, combine cooked quinoa, cherry tomatoes, red onion, cucumber, olives, feta cheese, olive oil, parsley, mint (if using), oregano, salt, pepper, and lemon juice. Toss gently to mix.
05 - Stuff each bell pepper generously with the quinoa mixture. Arrange peppers upright in the prepared baking dish.
06 - Cover with foil and bake for 15 minutes. Remove foil and bake for an additional 5 minutes, or until peppers are just tender and filling is heated through.
07 - Serve hot, garnished with extra herbs or a squeeze of lemon if desired.