Heat the olive oil in a deep, heatproof pot and briefly sear the tuna cubes, then remove and set aside.
In the same oil, sauté the finely chopped onion for 6-8 minutes.
Add the peeled, finely chopped tomato and mix.
Break the potatoes into thick pieces (snapped rather than cut sharply, so they release more starch), add them to the pot and pour in enough water to cover; salt lightly.
Crush the garlic, parsley and a little salt in a mortar, dilute with a little cooking water and pour into the pot together with the bay leaf and the hot pepper.
Cook over low heat for 30 minutes.
Add the green peas, the diced red pepper and the tuna, then cook for another 10 minutes and serve right away.