Preheat the oven to 200°C (400°F) and line a large baking tray with parchment paper. Drain the chickpeas into a sieve and rinse under cold water. Tip them onto a clean kitchen towel and pat very thoroughly until they are as dry as possible — this is the most important step for getting them crispy. Any moisture left on the surface will steam them in the oven instead of crisping them. Let them sit for a minute or two while you prepare the broccoli.