Preheat your oven to 180°C (350°F). Slice the tops off the peppers and carefully scoop out the seeds and membranes with a spoon, creating a hollow cavity. Place the peppers upright in a baking dish.
Bring a pot of water to a boil, then add the rinsed quinoa. Cook according to package instructions until fluffy, about 15 minutes. Drain and set aside.
While the quinoa cooks, heat the olive oil in a large skillet over medium heat. Add the chopped onion and cook, stirring occasionally, until translucent and fragrant, about 5 minutes. Then, stir in the minced garlic and cook for another minute until it smells aromatic.
Add the cooked quinoa, drained black beans, diced tomatoes, cumin, smoked paprika, salt, and pepper to the skillet. Stir well to combine and cook for another 5-8 minutes, until heated through and the flavors meld. The mixture should be slightly thick and fragrant.
Use a spoon to stuff each hollowed-out pepper with the warm quinoa mixture, pressing gently to pack the filling in tightly. Place the stuffed peppers upright in the baking dish, standing close but not overcrowded.
Bake the peppers uncovered in the preheated oven for 25-30 minutes, until they are tender and slightly blistered on the outside. You can check for doneness by piercing the peppers with a knife—if it slides in easily, they’re ready.
Remove the dish from the oven and let the peppers rest for 5 minutes. Garnish with freshly chopped parsley or cilantro for a burst of freshness and color.
Serve the stuffed peppers warm, straight from the oven, and enjoy the tender, flavorful filling with the slightly blistered, caramelized peppers on the outside.