Wash and dry the tomato

Cut the tomato into small enough pieces to fit in the food processor. (Seeding them is optional but preferred.)

Use the regular blade that came with the appliance, and do not overload the bowl with tomato pieces.

Press the pulse button to cycle the blade for two or three seconds.

Empty the bowl once you have diced the tomatoes to the desired size.

Repeat the process with a new batch.