Preheat oven to 400°. Line a rimmed baking sheet with parchment paper. Spray parchment paper with cooking spray.
Arrange mushroom caps, smooth side down, on prepared baking sheet. Sprinkle with salt.
In the work bowl of a food processor, pulse together pine nuts and sundried tomatoes until finely chopped. Add cream cheese, Parmesan cheese, and bread crumbs, pulsing until combined.
Spoon approximately 2 teaspoons pine nut mixture into wells of mushroom caps.
Bake until filling is golden brown, 12 to 15 minutes.
Garnish with pesto and fresh basil, if desired. Serve warm.
Notes
Make-Ahead Tip: Filling can be made several hours in advance, stored in an airtight container, and refrigerated. Fill and bake mushrooms just before serving.
Recipe by TeaTime Magazine at https://teatimemagazine.com/pine-nut-sundried-tomato-stuffed-mushrooms/