Preparing the tuna: Place the tuna cubes in a bowl.
Mixing the ingredients: In the bowl with the tuna, add the red onion, capers, lemon juice, chives and olive oil. Season with salt and pepper to taste. Mix gently to coat the tuna with all the ingredients.
Serving: Serve the tuna tartare very fresh, accompanied by slices of toasted bread for a crispy texture. You can also present it with a green salad for a touch of freshness.