Preheat your oven to 375°F (190°C).
Rinse the quinoa under cold running water and drain. In a medium saucepan, bring the vegetable broth to a boil. Add the quinoa, cover, and reduce the heat to low. Simmer for 15 minutes until the broth is absorbed and the quinoa is tender. Remove from heat and let it sit, covered, for 5 minutes.
While the quinoa is cooking, slice the tops off the bell peppers and remove the seeds and membranes. Arrange the peppers in a baking dish, cut-side up.
In a skillet, heat the olive oil over medium heat. Add the onion, carrots, and zucchini. Sauté for 5-7 minutes until the vegetables are softened.
Fluff the cooked quinoa with a fork and add it to the skillet with the vegetables. Stir in the chopped parsley, mint, salt, black pepper, and smoked paprika. Cook for an additional 2 minutes to blend the flavors.
Remove the skillet from heat and allow the mixture to cool slightly before stirring in the crumbled feta cheese.
Spoon the quinoa and vegetable mixture into the hollowed-out peppers, packing it in firmly.
Replace the tops of the peppers and bake in the preheated oven for 25-30 minutes, or until the peppers are tender and the filling is heated through.
Serve the stuffed peppers hot, with a drizzle of olive oil or a dollop of yogurt if desired.