Preheat the oven to 425 °F.
Cut up the vegetables and arrange the carrots on four 12-inch squares of aluminum foil
Rinse the salmon and pat it dry. Cut into 4 pieces, and lay each piece on top of the carrots.
Arrange the leeks and tarragon on top of the fish.
Sprinkle salt and pepper over the leeks and tarragon
Arrange the lemon slices on top
Wrap up the foil, crimping the edges to make a tight packet.
Pop it in the oven for about 15 minutes, until the salmon's internal temperature is 165 °F