Preheat oven to 400 degrees F and line 2 baking sheets with parchment paper.

In a large cast iron pan, heat 2 tablespoons of olive oil over medium high heat. Add the onions, shiitakes and peppers. Stir and sauté until vegetables are soft and slightly brown. Add garlic and thyme cook for another 2 minutes. Adjust heat if browning too quickly. Total time about 15 minutes. Season with salt and pepper. Set aside to cool.

On a lightly floured surface, unfold the thawed puff pastry and cut out 3 inch circles from the dough. Evenly space the circles on the baking sheets.

With a sharp knife, score around the perimeter of the circles about 1/4 inch from the edge.

Top the puff pastry rounds with a small spoonful of the sautéed vegetable mixture, keeping the mixture within the scored perimeter. Top with shredded Manchego cheese. Brush the edges of the tartlets with the egg wash.

Bake for about 20 minutes or until tartlets are golden brown. Garnish with thyme leaves.