Wash and dry the cucumbers.Slice them down the middle length wise.Using a spoon, gently scrape out the insides.Set aside.Drain the water from the tuna cans and scoop into a large bowl.Using a fork, gently mash the tuna until it is flaked.Add the celery, onion, Greek yogurt, mayo, mustard, salt and pepper. Add the fresh herbs if you plan to use any.Mash all of the ingredients together with a fork until everything is mixed together well.Place your fresh tuna salad mixture in each cucumber half.Top with sliced, homegrown tomatoes and additional salt and pepper to taste.Enjoy!