Start by draining and rinsing the chickpeas under cold running water. Let them drain well and add them to a large bowl.
Halve the avocado, remove the pit, and scoop out the flesh. Dice the avocado into 1-1.5 cm pieces and add them to the bowl immediately to prevent browning.
Crumble the feta cheese over the other ingredients in the bowl.
Peel and thinly slice the red onion into half rings and add to the bowl.
Finely chop the fresh parsley and mint, and add them to the bowl.
In a small bowl or jar, combine the fresh lemon juice and olive oil. Mince the garlic and add it along with the dried oregano.
Whisk or shake the mixture until well combined and season generously with salt and freshly ground pepper. Adjust seasoning to taste.
Pour the dressing over the salad ingredients and gently toss everything together, being careful not to mash the avocado.
The salad is best served right away, but you can refrigerate it for later. If preparing in advance, keep in mind that the avocado may brown slightly.