Line 2 rimmed baking sheets with parchment paper. Set aside.
In a medium bowl, toss mushrooms with 2 teaspoons olive oil. Spread mushrooms in a single layer on a prepared baking sheet, and sprinkle with salt.
Bake until mushrooms are tender and have released their liquid, 20 to 25 minutes. Let cool on baking sheet, and chop finely. Set aside.
In a large nonstick sauté pan, heat remaining 1 teaspoon olive oil over medium-high heat. Add pork, breaking apart into crumbles. Add garlic salt and black pepper. Add yellow bell pepper and onion, stirring and cooking until pork is browned and vegetables are tender, approximately 5 minutes. Drain pork mixture on paper towels. Transfer pork mixture to a bowl, and add mushrooms, stirring to combine. Let cool.
Increase oven temperature to 400°.
Let puff pastry thaw just enough to be able to roll up and encase filling. (It should still be cold and firm.)
Unroll both sheets on a lightly floured surface. Divide pork mixture evenly between puff pastry sheets, leaving a 1-inch margin around edges and pressing mixture lightly into pastry. Sprinkle each evenly with thyme leaves. Starting from a long side, roll up each sheet, firmly encasing pork mixture.
Cut each roll into ½-inch slices, and place 2 inches apart on remaining prepared baking sheet. Set aside.
In a small bowl, combine egg and water, whisking to blend. Brush slices with egg mixture.
Bake until golden brown, approximately 15 minutes.
In a small bowl, combine honey and mustard, stirring until blended. Brush warm pastries with honey mixture.
Garnish with thyme sprigs, if desired.
Serve immediately.
Recipe by TeaTime Magazine at https://www.teatimemagazine.com/pork-and-mushroom-puff-pastry-swirls-recipe/