Mushroom Pesto Sandwich

Bread,two slices
2 tbsp Pesto
4/5 Button Mushroom,sliced
Half Yellow Onions, sliced
A pinch rather than a handful of dried Rosemary & Parsley & Black Pepper
Salad leaves
1) Fry / sauté mushroom and onions until onions turn transparent or slightly brown on the edges. Season with herbs, black pepper & salt. 
2) Toast bread!
3) While toasting the bread, wash salad leaves and dry them thoroughly.
4) Place toasted bread on an empty plate, spread the pesto generously, layer with mushroom, salad leaves and some English mustard if you wish to make the sandwich more robust and then cover it with the other piece of bread.