Peel the cucumbers. If using English cucumbers, halve lengthwise and scrape out the seeds. Mediterranean cucumbers do not need to be seeded. Grate the cucumbers coarsely. Transfer to a sieve and sprinkle with 1 1/2 teaspoons salt. Toss well, then let drain 45 minutes. Put the cucumbers in a clean dish towel and squeeze well to remove excess water.
Grate the fennel coarsely.
In a bowl, combine the yogurt, herbs, garlic, chile, 1 tablespoon olive oil and 1 tablespoon lemon juice. Whisk well. Stir in the fennel and the cucumbers. Taste and adjust seasoning with salt and additional lemon juice, if desired. Refrigerate for at least 30 minutes or up to 3 hours before serving.
Transfer to a serving bowl or platter, drizzle with remaining 1 tablespoon olive oil and garnish with reserved herbs.