To prepare the avocado, hold it in one hand whilst using a sharp knife to cut it in half lengthwise to the pit. Twist and separate the halves. Start with the half without the seed first. Run a tablespoon under the flesh, but do not remove it. Slice the fruit lengthwise, then crosswise, then invert the fruit over a bowl, Keep the skin. Thrust the edge in the seed, twist and remove it. Use the leftover skin to remove the seed from the knife and toss it away. Prepare the second half as you did that first.

Combine the chopped tomato with the avocado and toss.

Serve immediately.