Start by preheating the oven to a moderate temperature, usually around 350°F (175°C). While the oven is heating, prepare the sweet peppers for the filling. Choose firm, colorful bell peppers, carefully cut off the top, and remove the seeds and membranes from the inside. In a mixing bowl, prepare the filling mixture. Combine cooked quinoa or brown rice with black beans, corn kernels, diced tomatoes, chopped cilantro and a portion of soaked chia seeds. Season the mixture with your choice of spices, such as cumin, paprika, chili powder, salt, and pepper for added flavor.
Once the filling is well mixed, generously fill each hollowed bell pepper with the quinoa or rice mixture, packing tightly to ensure they are well stuffed. Place the sweet pepper in a baking dish, cover it with aluminum foil, then place it in the preheated oven. Bake the stuffed sweet peppers for about 30-40 minutes. Once done, remove the foil and serve.