Prepare the chickpeas: Drain and rinse the chickpeas in a colander. Shake off excess water and set aside.
Chop the vegetables and herbs: Thinly slice the red onion; dice the cucumber (removing seeds if watery); halve the cherry tomatoes. Roughly chop the parsley (and mint or dill, if using).
Make the dressing: In a small bowl or jar, whisk together lemon juice, red wine vinegar, Dijon mustard, garlic, and oregano. Slowly drizzle in the olive oil while whisking to emulsify. Season with salt and pepper, then taste and adjust as needed (add a bit more lemon or honey if needed).
Assemble the salad (without avocado): In a large bowl, combine the drained chickpeas, sliced onion, cucumber, tomatoes, and herbs. Pour about two-thirds of the dressing over this mixture, tossing gently to coat.
Add the feta: Crumble the feta over the salad and gently fold it in so it mixes but doesn’t fully disintegrate.
Add the avocado: Cube the avocados and, if you like, lightly sprinkle with a little lemon juice to prevent browning. Add the avocado to the salad and very gently fold everything together, being careful not to mash the avocado.
Finish & serve: Taste the salad and add more of the reserved dressing if needed. Garnish with toasted seeds, a little extra parsley, and a final drizzle of olive oil. Serve immediately or slightly chilled.