2 Arrange walnuts on a lined baking sheet. Toast for about 10 minutes, or until golden and fragrant.
3 Meanwhile, wipe dirt of mushrooms with a damp cloth. Carefully remove the stems.
4 Dump walnuts into bowl of a large food processor. Place mushrooms hole side up on the baking sheet and bake for 15 minutes.
5 Meanwhile, pulse walnuts until finely chopped. Add basil, spinach, garlic, lemon juice, and salt. Pulse until well combined. Use a spatula to scrap down the sides. Add hummus and blend until fully combined.
6 Spoon mixture evenly into center of mushrooms. Arrange mushrooms on baking sheet and bake for 10 minutes.