Using the same sauté pan, fry the red pepper, green pepper and green chilli until slightly softened (about 6 minutes). You shouldn't need any additional oil as there will still be some left in the pan from frying the rösti. Once softened, remove the peppers from the pan and into a bowl. Place to one side while making the sauce.
Add coconut oil to the pan. Once melted, add 1 tablespoon wholemeal flour and the Mexican Spice Mix and stir continuously for 1 minute. Now, add the coconut milk and stir well to combine. Bring to the boil to thicken, stirring frequently (about 2-4 minutes).
Once thickened, turn the heat down to a gentle simmer and add sweetcorn, fresh coriander, juice of the lime and the cooked peppers. Give everything a good stir.
Now, gently stir the fish into the sauce until it's well coated. Let the sauce and fish simmer away for 15 minutes or until all the fish is thoroughly cooked through.
When the fish is cooked, spoon the pie sauce into four individual pie dishes. You can serve directly on plates if you'd rather. Place a sweet potato rosti on each portion and tuck in!