Slice the baguette in half lengthwise and remove some of the inside from the bottom half to create a 'trough' for the filling (use this to make breadcrumbs, which you can freeze). Brush both halves with some of the olive oil, then rub each with the garlic. Line the half with the trough with the basil leaves.
In a bowl, combine the tuna, olives, pepper, onion, parsley, artichoke. Make the vinaigrette by whisking the lemon juice and the remaining olive oil. Pour over the tuna mixture and stir. Season to taste with the salt and pepper.
Spoon the tuna mixture over the bread with the basil leaves - and serve!