Preheat your oven to 180°C (350°F).
Wash the peppers thoroughly, then slice each in half lengthwise and remove the seeds and membranes.
Cook the quinoa according to package instructions, usually simmering in twice its volume of water until fluffy and water is absorbed, about 15 minutes. Fluff with a fork and let it cool slightly.
In a mixing bowl, combine the cooked quinoa, diced tomatoes, chopped herbs, nutritional yeast, and season with salt and pepper. Drizzle with a little olive oil and stir everything together until well mixed.
Stuff each pepper half generously with the quinoa mixture, pressing down slightly to pack the filling in.
Arrange the stuffed peppers in a baking dish, cut side up. Drizzle the tops with a little olive oil to encourage browning.
Cover the dish loosely with aluminum foil to keep moisture in, then bake for 30 minutes. The peppers should become tender and slightly blistered on the edges.
Remove the foil, sprinkle the nutritional yeast or vegan cheese on top, and bake uncovered for an additional 10 minutes until the tops are golden and bubbling.
Once baked, let the peppers rest for about 5 minutes, allowing the flavors to settle and the filling to firm up slightly.
Serve the stuffed peppers warm, perhaps with a squeeze of fresh lemon or a side salad for a complete meal.