Combine cilantro sprigs, ginger, garlic, and chiles in a resealable plastic freezer bag; seal. Lightly pound with a skillet or rolling pin until ginger and garlic are well mashed.
Add cucumbers, 1 teaspoon salt, and sugar. Seal bag; shake to mix. Squeeze bag firmly to slightly mash cucumbers, 1-2 minutes. Place bag in a large bowl; let macerate at room temperature, turning halfway through, until juices form, about 35 minutes.
Empty contents of bag into bowl; turn bag inside out and scrape out any small bits. Discard cilantro sprigs. Mix in celery, juice, and oil. Season with more salt, if desired.
Divide avocado among plates; spoon salad over. Garnish with chopped cilantro and basil.
Per serving: 190 calories, 15 g fat, 8 g fiber Nutritional analysis provided by Bon Appétit