Drain the 400g chickpeas (1 can). Set aside a few whole chickpeas for garnish. Pat the chickpeas dry if very wet. Cut the 1 ripe avocado in half, remove the pit, scoop out most of the flesh and reserve a few small pieces for garnish; roughly chop the remaining avocado.
Add the drained chickpeas, chopped avocado (not the reserved pieces), 1 handful of fresh spinach, 1 clove of garlic (peeled), juice of ½ lemon, 1 tsp ground cumin, and 1 tsp salt to a blender or food processor.
Add 3 tbsp of the 3–4 tbsp olive oil and 3 tbsp of the 3–4 tbsp cold water to the blender. Blend on high for about 1 minute.
Stop, scrape down the sides with a silicone spatula, and check texture and seasoning. If needed, add up to 1 more tbsp cold water (to total 3–4 tbsp) and blend until smooth. Adjust lemon juice or salt to taste.
Transfer the avocado hummus to a serving bowl. Top with the reserved whole chickpeas and reserved avocado pieces, drizzle the remaining olive oil (the rest of the 3–4 tbsp), and sprinkle za’atarto taste and coriander leaves over the top.
Serve immediately with toast, grissini, or tortilla chips.