Preheat the oven to 190°C (Gas Mark 5 / 375°F).
Boil the quinoa in the vegetable stock for around 15 minutes - the quinoa should become soft and the spiral-shaped germ should detach, and the liquid should all be absorbed. If the liquid begins to dry up before the quinoa is ready, just add a dash more water and mix well. When the liquid is nearly gone, you will need to turn the heat down fairly low to prevent the quinoa from sticking to the bottom of the pan.
While the quinoa is cooking, heat the oil in a large frying pan, and add the garlic, onion and red pepper. Cook over a medium heat for 5 minutes, until the vegetables are almost soft. Remove from the heat, and add the spring onions, sweetcorn, drained black beans and fresh coriander. Stir in the enchilada sauce and the cooked quinoa, and then add the spices as necessary (if your sauce was particularly spicy you might decide to skip the additional chilli powder). Season to taste, and mix well to combine.
Transfer the mixture to a large baking dish, and sprinkle over the grated cheese. Bake for around 30 minutes, or until the cheese is golden and crispy, and the quinoa mixture is piping hot.