Heat the oil in a paella pan or a wide-bottomed non-stick frying pan. Sauté the onions and garlic. Add the peppers and chilli pepper, cook briefly. Add the rice, sauté and stir until translucent. Pour in the wine and reduce completely. Add the stock and saffron, cover and simmer gently for approx. 10 mins., stirring occasionally. Cut the reserved onion greens into thin rings, stir in. Salt the fish pieces, calamari and prawns, carefully mix into the rice. Cover and simmer over a low heat for a further 10 mins. Scatter the mussels over the paella. Cover and simmer for a further 5 mins. until the mussels open. Drizzle a little olive oil over the paella and arrange the lemon wedges on top.