Preheat your oven to 220°C (430°F) and line a baking sheet with parchment paper.
Wash the bell peppers thoroughly, then slice each one in half lengthwise, carefully removing the seeds and membranes. Keep the halves intact for stuffing.
Place the peppers cut side up on the prepared baking sheet and drizzle with olive oil. Rub gently to coat evenly, then roast in the oven for about 20-25 minutes, until the skins blister and blacken in spots.
While the peppers roast, combine the cooked quinoa, drained black beans, tomato paste, cumin, smoked paprika, chopped cilantro, and a drizzle of olive oil in a large bowl. Mix until well combined and season with salt and pepper to taste.
Once the peppers are roasted and blistered, remove them from the oven and allow to cool slightly for about 5 minutes. The skins will be smoky and slightly charred, adding depth to the flavor.
Carefully spoon the filling into each roasted pepper half, pressing gently to pack in the mixture. Place the stuffed peppers back onto the baking sheet.
Bake the stuffed peppers for another 10-15 minutes at 180°C (355°F), until the filling is heated through and slightly golden on top.
Remove from the oven and let rest for 5 minutes to allow flavors to settle. Serve warm, garnished with extra cilantro if desired.