Line a rimmed baking sheet with parchment paper. Set aside.
Let puff pastry sheet thaw until it is pliable but retains some firmness. (It will be easier to roll up this way.) Place on a work surface, and sprinkle with olives, walnuts, thyme, cheese, and pepper, leaving a 1-inch border around edges of pastry sheet.
Beginning at one short end, roll up firmly, encasing ingredients. Using a serrated knife, cut roll into ½-inch slices. Place slices 2 inches apart on prepared baking sheet.
In a small bowl, combine egg and water, whisking well. Brush tops of slices with egg wash.
Bake until golden brown, 13 to 15 minutes.
In a small bowl, combine mustard and honey, stirring to blend. Brush warm pastries with glaze.
Garnish each with a fresh thyme sprig, if desired.
Serve warm.
Notes
Make-Ahead Tip: Puff-pastry roll can be made earlier in the day, wrapped in plastic wrap, and refrigerated until shortly before serving. Slice before baking.
Recipe by TeaTime Magazine at https://teatimemagazine.com/walnut-olive-palmers-recipe/