Hold the tomato on its side on a sturdy surface. Insert the end of a sharp paring knife 1 inch into the tomato just outside of the core. Rotate the tomato as you cut around the core to remove it from the tomato.
Place the top of the tomato, where you removed the core, down onto a cutting board if it is a seedless variety. If the tomato contains seeds, slice it in half, and then lay the cut side down onto a cutting board. Cut the tomato into parallel slices to your desired thickness. Slices that are 1/4 to 1/2 inch are ideal for chopping tomatoes.
Set the end pieces of the tomato off to the side. Stack one tomato slice on top of another. Cut the stacked tomatoes into strips that are no wider than 1/2 inch. Rotate the strips and cut them crosswise to make cubes.
Stack the end pieces on top of each other with the skin side facing down. Cut these into 1/2-inch strips to create chopped cubes.