In a mortar with a pestle, pound garlic, ginger, fennel seeds and ½ tsp salt into a rough paste. Add paprika and chilli flakes and pound a little more.
Pod the peas. Remove woody ends from asparagus and cut into 2-3cm lengths.
Season fish fillets with ¼ tsp salt. Heat 1 tbsp oil in a deep frying pan over a high heat and when hot, sear fish on both sides to get a nice crust. Remove and set to one side. Heat remaining oil in pan and add onion, chorizo and ¼ tsp salt. Cook for 5 minutes, then add the spice paste and cook for 2 more minutes. Deglaze with wine and simmer for a few minutes.
Add the peas, asparagus, stock and clams, then bring to a simmer for 2 minutes. Return fish to the pan and simmer, covered, for another 3-5 minutes, until the fish has cooked through and the clams have opened. Remove from the heat and gently stir through the butter. Give a good grind of pepper, taste for seasoning and stir through the parsley.
Divide fish among four bowls, spoon the juices and clams over the fish and serve immediately, with a couple of extra bowls for discarding the clam shells.