Preheat the oven to 200 degrees C. Pulse the tomatoes in a food processor or blender until smooth. Add chilli powder to taste, then set aside.
Heat the oil in a large frying pan, add the spring onions and garlic and sauté for 1 minute. Stir in the seafood, then add 150ml of the puréed tomatoes and 1 tablespoon of the cream and heat through. Transfer to a bowl and keep warm.
Pour the remaining tomatoes and cream into the frying pan and bring to a simmer, then reduce to a gentle simmer.
Dip one tortilla at a time into the sauce in the frying pan for 10 seconds until just pliable. Allow any excess sauce to drip off, then lay on a board and top with a spoonful of the seafood mixture. Roll up and place, seam side down, in a large baking dish, measuring about 18 × 28cm. Repeat until you have eight enchiladas.
Stir any remaining seafood mixture into the sauce in the frying pan and pour over the tortillas. Sprinkle with cheese and jalapeños. Bake for 20 minutes. Season, then serve.