Fresh and green, this sauce is a perfect accompaniment to grilled fish.
In a medium bowl, mix half the zucchini, half the cucumber, the celery, green pepper, scallions, garlic, jalapeno, parsley, oil, sherry vinegar, hot sauce, 1 tablespoon lemon juice, and salt and pepper. Cover with plastic; refrigerate overnight.
Preheat oven to 400 degrees. Place tomatillos on a rimmed baking sheet; roast until softened and browned in spots, about 25 minutes. Roughly chop; add to bowl of marinated vegetables with remaining zucchini and cucumber. Return bowl to refrigerator to chill 2 to 3 hours.
Blanch basil in boiling water 30 seconds; transfer to blender, and add marinated vegetables, avocado, and rice-wine vinegar. Puree while slowly adding stock. Season with remaining lemon juice, salt, and pepper. Refrigerate, covered, until ready to serve, up to 1 day.