Bring a large pot of water to a boil; season with salt. Cook pasta 1 minute less than packaged directions. Drain and toss pasta with 1 tablespoon of olive oil in a large mixing bowl. Place pasta on a sheet tray to cool down.
Combine mustard with lemon juice and zest in a separate large mixing bowl. Drizzle in the remaining olive oil slowly to make a creamy dressing; season with salt and black pepper. Add pasta, tomatoes and mozzarella, stir to combine.
