Wash, clean, quarter and seed the tomatoes. Cut the tomatoes into slices. Wash basil, dab dry and tear larger leaves roughly. Mix the tomatoes, 2 tablespoons of olive oil and basil.
Season with salt, pepper and 1 pinch of sugar. Drain the tuna. Mix tuna with lemon juice and capers. Season with salt and pepper. Drain olives and chop finely. Wash parsley, dab dry and chop finely.
Mix olives, parsley and 2 tablespoons of olive oil. Season with pepper. Cut bread into 12 slices. Place on a baking tray and roast in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 15 minutes until golden brown, turning once.
Take out and spread with 2 tablespoons of olive oil. Peel and halve the garlic. Rub slices of bread with the garlic halves. Spread the prepared mixture over 4 slices of bread. Serve garnished with basil and lemon.