Heat a sauté pan and melt the butter with the oil over high heat.
Add the onion and cook for two minutes until softened.
Stir in the garlic, diced pancetta, carrot, celery, leek, and bay leaf and cook for two more minutes.
Pour in the lentils and 175ml of red wine and bring the mixture to a boil.
Simmer until the wine has reduced by half, then add 450ml of chicken stock.
Cook the lentils for 25 to 30 minutes until tender.
Stir in the sherry vinegar and fresh parsley.
Season the monkfish fillets with salt and black pepper.
Sear the monkfish in a smoking hot frying pan with olive oil for 1 to 2 minutes per side.
Let the fish rest on a warm plate for 3 minutes before slicing into four pieces.
Divide lentils into four bowls, top with sliced fish, and garnish with cooked pancetta slices and cress.