Preheat the oven to 200°C/fan 180°C/gas mark 6. Drain and rinse the can of chickpeas and set half of them aside. Pat dry the other half and toss with the smoked paprika, cumin, coriander, cayenne pepper and ½ tbsp olive oil. Season and spread out on a roasting tray. Cook for 30 minutes, turning over halfway through, until crispy.
Meanwhile, place the remaining half of the chickpeas in a food processor with 2 tbsp olive oil, 2 tbsp tahini, the lemon juice, garlic and seasoning. Blend and add a splash of water if it seems too thick. Transfer to a bowl and stir through the harissa paste.
Combine the yogurt with the remaining tahini. Add some seasoning and set aside.
Halve the avocados and remove the stones. Brush the flesh side with 1 tbsp olive oil, then place these on a hot barbecue or griddle pan for 4-5 minutes until there are dark golden griddle marks all over the flesh side. Transfer to a serving plate and fill them with the houmous, then top with the roasted chickpeas. Dollop the remaining harissa over as a garnish, then sprinkle over the coriander. Serve with tahini yogurt on the side.