Preheat the grill to a medium-high heat. Put the turkey meat, onion, carrot, sweetcorn and herbs into a large bowl. Season with some pepper and mix together – you can do this with your hands if you like.Grill the burgers for 12 to 15 minutes, turning them over once, until browned and cooked through. Remove from the grill and let rest for a couple of minutes.While the cooked burgers are cooling, lightly toast the burger buns under the grill on the cut side only. Put some lettuce on the bottom halves and place the burgers on top. Add 2 slices of tomato onto each one and cover with the top half of the bun.