1. Peel, quarter and seed the tomatoes.
2. Cut the ends off the Espelette pepper and remove the seeds; chop into small pieces.
3. Peel and cut up the onions.
4. Peel and chop the clove of garlic.
5. Cut the ham into thin strips.

Preparing the "basquaise" garnish

1. Heat half the olive oil in a Dutch oven.
2. In the hot oil, sweat the garlic gently; sauté the ham; add the onions and cook without letting them color; add the Espelette peppers and combine well.
3. Cover and cook for 15 minutes over low heat, stirring occasionally.
4. After this initial cooking time, add the quartered tomatoes; cover and cook another 15 minutes, stirring every 2 or 3 minutes.

Cooking the tuna and Presentation

1. Season the tuna medallions with salt and pepper on both sides.
2. Place the remaining olive oil in a skillet; heat the pan and sear the tuna medallions for approximately 2 1/2 minutes on each side.
3. When the tuna is cooked, transfer to a plate and let rest, covered with a piece of aluminum foil, for at least 5 minutes. (Place in the oven for 2 minutes to reheat just before serving.)
4. Correct the seasoning of the "basquaise" garnish.
5. Arrange the tuna medallions on a bed of "basquaise" garnish and sprinkle with sprigs of chervil.