Bring a saucepan of water to boil on high. Add the vinegar. Crack 1 egg into a small bowl. Use a large spoon to swirl water to make a whirlpool. Carefully pour the egg into the centre of the whirlpool and poach for 1-2 minutes for a soft egg. Use a slotted spoon to transfer to a plate. Cover loosely with foil to keep warm and repeat with remaining eggs.
Place rocket, lemon juice, oil, salt and pepper in a bowl and toss well. To serve, place 1 slice of hot toast on each plate and top with rocket, ham slice and a poached egg. Season to taste.
The vinegar will assist in keeping the egg together. Using the freshest eggs possible will also help.