Rinse, trim, and coarsely chop the tomatoes. Rinse, trim, and finely dice the celery. Rinse the mint and basil, pat dry, and finely chop.
Puree the tomatoes, celery, and lemon zest in a blender or with an immersion blender. Pass the puree through a fine strainer. Mix in the mint, basil, and lemon juice, then season to taste with salt and chili powder. Fill 4 glasses with 1 ice cube, then pour in the juice. Garnish with the celery leaves and serve.