Preheat the oven to 180C/350F/Gas 4.
For the mushroom on toast, drizzle three tablespoons of the oil over the bread and place onto a baking sheet. Place in the oven to toast for 3-4 minutes, or until golden-brown and crisp.
Heat the olive oil in a pan and fry the mushrooms for 2-3 minutes, then season with salt and freshly ground black pepper.
For the pesto, place all of the pesto ingredients into a food processor and pulse until smooth.
Serve the mushrooms on the toast, with the pesto drizzled over the top.