Heat 1 tbsp oil in a large frying pan over a medium heat, add the leeks and fry for 5-6 mins until softened.
Add the mushrooms, increase the heat to medium-high and fry for 8-10 mins until golden and tender and any water has evaporated.
Stir in the garlic and oregano; season and fry for 1 min more until the garlic is fragrant.
Meanwhile, heat the remaining oil in a separate frying pan and fry the breadcrumbs over a medium heat for 3-4 mins, stirring frequently, until crunchy and golden. Season, transfer to a plate and set aside.
Bring a large pan of salted water to the boil and cook the spaghetti to pack instructions; drain well.
Stir into the mushrooms and leeks and toss well.
Stir in the lemon zest and juice, then scatter with the basil and crispy breadcrumbs to serve.
