Pull the stems off the mushrooms and chop finely, leaving the caps whole. Place these on an oven tray drizzled with half the oil and season. bake or grill for 7 min at 200C or until they begin to soften. Remove and let cool.
Make a paste by chopping together the white part of the spring onions, garlic, and anchovies. Sauté gently in the other half of the oil until fragrant. Now add the chopped mushroom stems and cook until a little soft. Take of the heat then stir through the feta, herbs and trout. Let the mixture cool slightly then quickly blend, keeping it slightly textured.
Place in a piping bag and pipe about one teaspoon of mixture into the mushrooms (straight down, not swirled.) Garnish with baby basil leaves.