Slice the tomato into two halves along its length.
Lay down each half, and slice off the top bit.
Slice it along its length again.
While slicing, make sure you are holding the tomato gently. If you apply too much pressure on it, all the juices will squirt out making the whole process a bit messier.
Turn the half through 90 degrees, and slice it again. Therefore making the cuts perpendicular to your original slices.
I’m pleased to inform you, that you have just chopped a tomato.