Preheat the grill to medium-high. Put the eggs in a saucepan, cover with cold water and bring to the boil. Cook for 8 minutes, then drain and cool under cold water. Peel and cut into quarters.
While the eggs are cooking, make the dressing and the croutons: whisk the olive oil, lemon zest and juice and Dijon mustard together in a small bowl. Put the torn baguette pieces on a baking tray and toast under the grill for 2-3 minutes, until just golden.
In a large bowl, toss together the ham, cherry tomatoes, baby gem lettuce, quartered eggs and croutons. Drizzle with the dressing and serve.