In a small pot add potatoes, cover with water and bring to a boil. Let simmer for approximately 15 minutes or until potatoes are tender. Remove from heat, add peas and cover with a lid.
Meanwhile remove the skin from the Chorizo sausage. Slice lengthwise into quarters and then cut into 1/4 inch pieces. Season the haddock to taste with salt and pepper.
To a medium size frying pan add olive oil and over medium heat bring oil to temperature. Add the Chorizo and fry for 1-2 minutes until golden brown and crispy. Remove Chorizo and set aside.
To the same pan add the haddock and cook for about 3 minutes per side (depending on the thickness of the fillet) or until fish is cooked through and begins to flake easily. Remove from pan, cover with foil and set aside.
Drain the peas and potatoes and stir in the pesto.
Spoon the pesto peas and potatoes onto serving plates and top with haddock fillets. Sprinkle Chorizo over the top and garnish with basil leaves if desired.