Melt butter in a frying pan. When sizzling add the breadcrumbs. Cook, stirring constantly, until golden brown.Remove from the heat and place in a small bowl with the lemon zest and parsley. Season to taste and mix well. Set aside. Heat a drizzle of olive oil in a large frying pan.Add the onion and cook until tender. Add the garlic and cook until fragrant.Add the drained beans, fresh thyme and stock. Bring to a simmer. Simmer until the beans are very tender and the liquid has reduced. Crush a few beans as you stir to add more body to the sauce. Switch the heat off and add the lemon juice and dill. Stir. Heat the butter with a little drizzle of olive oil in a large frying pan. Add the sliced mushrooms and cook on high heat until just golden brown and still juicy and tender. Season well with salt and pepper. Brush the slices of sourdough with olive oil and season with salt. Pan fry until golden brown and crisp on both sides. Stir the mushrooms into the beans just before plating up. Serve generous spoonfuls of mushrooms and beans over the sourdough.Finish with a sprinkle of the crispy, crunchy lemony breadcrumb topping and fresh dill sprigs.