Preheat the oven to 375 degrees F (190 degrees C). Fit pie pastry into a 9-inch pie dish. Poke holes in bottom of crust with a fork.
Spread mustard evenly over bottom of crust. Cover with Swiss cheese, then arrange tomato slices over top to cover cheese in a spiral, from the outer edge to the center. Drizzle oil over tomatoes and sprinkle herbes de Provence over top.
Bake in the preheated oven until crust is golden brown, cheese is melted, and tomatoes are curled at the edges, about 20 minutes.