Preheat the oven to 180 °C (350 °F).
In a large bowl, combine flour, salt, and butter. Work the mixture until it resembles coarse sand. Gradually add cold water and mix until a dough comes together. Knead briefly to obtain a smooth dough, form a ball, wrap tightly in plastic wrap, refrigerate for 1 hour, or place in the freezer for 10-15 minutes.
Roll out the dough on a lightly floured surface. Transfer it to a greased tart tin or one lined with parchment paper. Remove excess dough and prick it with a fork to avoid air bubbles.
Line the crust with parchment paper and fill it with pie weights. Blind bake for 15 minutes
In a small bowl, whisk together eggs, milk, salt, and pepper. Stir in chives and grated cheese until well mixed.
Thinly slice the tomatoes and place them on kitchen paper to remove excess moisture.
Spread Dijon mustard on the bottom of your quiche crust. Add the drained canned tuna on top. Pour the egg mixture over the tuna. Cover with tomato slices.
Bake the quiche in the oven for 30-35 minutes until the pie crust is cooked and the top turns golden brown. Let cool on a wire rack.
Finish with a drizzle of olive oil and chives on top.
