Pour broth into a 10- to 12-inch skillet over medium-high heat. Add onion, coriander, cumin and mustard seeds, chile flakes and bay leaf. Set celery hearts in pan, cover, and simmer until celery is tender-crisp when pierced, 7 to 10 minutes. Gently turn celery over after about 4 minutes to cook evenly.
With a wide spatula, carefully transfer celery to a rimmed dish. Pour broth through a fine strainer set over a bowl; discard bay leaf, but reserve seeds and onion.
Return strained broth to pan; stir in turmeric. Boil until reduced to about 2 tablespoons, 10 to 12 minutes. Stir in lemon juice, olive oil, and onion-seed mixture. Season to taste with salt and pepper. Pour broth mixture over celery in dish. Chill at least 2 hours or up to 1 day.
To serve, divide lettuce equally between four plates. Set a celery heart on lettuce on each plate; spoon liquid equally onto salads. Garnish with tomatoes.
Nutrition information per serving:
Calories122Fat8 gSodium612 mg