Slice the baguette lengthwise in half. Remove pieces of the inside of the bottom half to creata extra room for the sandwich filling. This should create a shallow trough.
Brush the inside of each half of the baguette lightly with olive oil. Place the basil leaves in the trough along the bottom half.
In a medium bowl, mix together the olive oil, minced garlic, tuna, roasted red peppers, green beans, artichokes hearts, kalamata olives, lemon juice, red onion, and flat-leaf parsley. Season with salt and black pepper to taste.
Scoop the tuna salad onto the bottom half of the bread, over the basil. Pour any extra dressing over the salad to help soften the bread.
Place the top piece of bread over the sandwich. Wrap the sandwich tightly in plastic wrap. Place the sandwich in the refrigerator to marinate for at least 6 hours or overnight. For best results, weigh the sandwich down while in the refrigerator with a heavy skillet or cans.
After the sandwich has marinated, slice diagonally into portions.
Serve or pack for lunch.