Heat some olive oil in a casserole and gently cook the onion in low heat for 15 min until the latter becomes transparent but not brown. Add the garlic, carrot and the capsicum. Cook for 5 more minutes.
Peel the potatoes and break them (cascar) into medium pieces inside the casserole. It is very important to break them rather than cut them so that the potatoes starch gets released and the sauce thickens. Cook for 2 to 3 minutes.
Add the tomatoes, the ‘choricero’ peppers, the paprika and the white wine. Stir in everything and then let the alcohol evaporate.
Pour enough fish stock to just cover the ingredients.
Season to taste and cook for 35 to 40 minutes over medium to low heat or until the potatoes are cook.
Remove the casserole off the heat and add the tuna so that it cooks with the residual heat. Cover and leave for 5 to 10 minutes.
Taste it, adjust the seasoning if necessary and add some finely chopped fresh parsley on top.