Prepare the vegetables: Dice 3 ripe tomatoes, diced, 1 cucumber, diced, and 1 green bell pepper, finely diced into small even cubes. Finely slice 1 small red onion, finely sliced. Place everything in a large salad bowl.
Add olives and capers: Add 60 grams pitted black olives and 1 tablespoons capers (optional) if using. Toss gently to combine.
Make the dressing: In a small bowl, whisk together 3 tablespoons extra-virgin olive oil, 2 tablespoons fresh lemon juice, 0.5 teaspoons salt, 0.3 teaspoons black pepper, and 1 teaspoons harissa (optional, for heat) if using. Taste and adjust seasoning.
Assemble: Pour the dressing over the vegetables and toss gently. Top with 240 grams canned tuna in olive oil (e.g. El Manar), drained and flaked, flaked into generous chunks. Arrange 2 hard-boiled eggs, cut into quarters around the edges of the bowl for presentation. Do not stir after adding the tuna and eggs — keep the layers visible.
Rest and serve: Let the salad rest for 10 to 15 minutes
before serving — this allows the flavors to meld. Serve with fresh crusty bread or as a side dish to grilled meats.