Soak the barley in enough cold water to cover for 30 minutes and drain well.
Bring the barley and enough water to cover to a boil. Reduce and simmer until tender, 40 minutes. Strain, transfer to a bowl of ice water, let cool for 1 minute. Strain again, letting water drain from barley.
Combine barley, tomato, cucumber, parsley, mint and scallions in a large mixing bowl. Stir in the olive oil, lemon juice, salt and pepper.
Cut the core from the cherry tomatoes and make two cuts in the tomato to open it up like a flower. Stuff each tomato with some of the salad, and serve on a chilled platter.
(Note: Barley can be prepared up to 2 days in advance, tomatoes can be stuffed up to 6 hours in advance.).