Core the tomatoes to remove the watery center. Chop the outside into small chunks and set aside.
Heat olive oil in a pan over medium heat and saute the chopped onion for a few minutes until light golden brown.
Add the chopped tomatoes , garlic powder, chopped dates, Worcestershire sauce and chopped basil. Saute for 2-3 minutes.
Allow the mixture to cool down for a few minutes and spoon it into a cookie cutter set on a serving plate as shown. Remove the cutter gently and serve.
Notes
The quality of tomatoes you use will make a huge difference in the flavor and texture of the tartare. Pick tomatoes that are bright red, ripe, juicy and firm.
I decided to core the tomatoes to remove their watery, soft inside. If you're using tomatoes with low moisture content, you can skip that step.