Wash cucumbers, peel if skin is thick or waxy
Dice into ½-inch cubes, scoop out seeds if very seedy
Cut avocados in half, remove pit, scoop flesh, dice into ½-inch cubes
Slice red onion very thinly
Optional: soak onion in ice water 5 minutes, drain, pat dry for milder flavor
Chop cilantro, dill, and parsley
Make dressing: whisk olive oil, lemon juice, zest, garlic, Dijon, salt, pepper, sugar in bowl
Or combine in jar and shake
In large bowl, gently combine cucumbers, avocados, onion, tomatoes if using, herbs
Drizzle dressing over salad
Toss very gently to coat without breaking avocado
Taste and adjust seasoning
Serve immediately for best texture