Lay out 4 rashers of pancetta, slightly overlapping them. Place a piece of cod on top, generously season with black pepper, then roll and wrap in the pancetta, and repeat.
Place in a large non-stick frying pan on a medium heat and cook for 8 minutes, turning occasionally, adding the rosemary for the last 2 minutes.
Remove the fish to a plate. Toss the lentils into the pan with 1 tablespoon of red wine vinegar and push to one side to reheat for 1 minute and pick up all that residual flavour, while you quickly wilt the spinach with a splash of water alongside.
Taste, season to perfection with sea salt and pepper, and divide both between your plates.
Sit the wrapped cod on top of the lentils with the rosemary, and drizzle with 1 teaspoon of extra virgin olive oil.