Preheat the oven to 350°F (180°C) fan-forced. Place two of the garlic cloves on a baking tray and roast for 20 minutes, or until the garlic is soft.
Turn the oven down to 210°F (100°C). Cut the third garlic clove in half and rub the cut sides over the bread slices. Cut the bread into cubes, place on the baking tray and bake for 5 to 10 minutes, until the bread croutons start to dry out and take on a bit of colour. Set aside.
Place the pancetta on a sheet of foil under an oven grill (broiler) preheated to medium–high, and grill until the pancetta starts releasing its fat and turns a deep pink. Keep an eye on it, so the edges don’t burn – it should take no more than 5 minutes if the slices are thin. The pancetta will be a bit soft when hot, but will crisp up as it cools. Set aside.
Wash and spin-dry the lettuce leaves, discarding any damaged ones. Chop or tear the leaves into large pieces and place in a mixing bowl.