1. Put a heavy based casserole dish with a lid on medium to high heat and add the olive oil. Add the chopped chicken breasts and until they start to brown, then add the chorizo and let that brown a little too. Set aside, leaving the oil in the pan.
2. Add onions to the oil, and soften them, then add garlic, peppers, celery, green chillies, thyme and oregano and stir through. Return the chicken and chorizo to the pan; add the onion and garlic salt, paprika, cayenne and mustard powder and pepper. Then add the rice, tomatoes and stock, give it a good stir. Bring to the boil and let it simmer covered for approximately 15 minutes until the rice is cooked through.
3. Give it a good stir every now and then so it doesn't stick. Now add the prawns and cook for a few minutes, then add the mussels and the clams and cover again for about 2-3 minutes or so or until the shells have opened.
4. Sprinkle with the parsley and the spring onions and serve.