Bring water to a boil in a medium saucepan.

Add eggs and cook for 7 minutes on medium-high heat.

Drain and cool eggs before peeling and slicing width-wise.

Peel potatoes and slice into french fry-sized pieces.

Heat vegetable oil in a frying pan.

Add potatoes and fry until golden, turning occasionally.

Remove from pan and place on a paper towel-lined plate to absorb excess oil.

Salt the potatoes while still hot.

Chop cucumbers, tomato, and onion for the salad.

Mix chopped vegetables in a bowl with olive oil, salt, and pepper.

Slice the baguette lengthwise, stopping before cutting it completely in half.

Spread harissa on both sides of the baguette.

Spoon the Tunisian salad onto the bottom half of the baguette.

Distribute the tuna evenly on top of the salad.

Place the sliced egg on top of the tuna.

Add french fries and/or capers to the sandwich, if desired.

Place the top half of the baguette in place.

Serve with olives.