The #1 crispy tip is to rinse, drain really well, then dry really well. Like, really, really well. The less moist (ew, sorry) the chickpeas are, the crispier they will become!
#2: Peel the skins!
Peeling the skins is onerous and annoying. Yes, I know. But in my experience, it does help them crisp up a bit more in the oven. And when it comes to crisping chickpeas, every little bit helps!
#3: You’ll want to wait to add any other seasonings until after they’re done baking. I’ve found that too much seasoning can interrupt the crisping process, almost by trapping in the moisture and not letting the chickpeas “breathe.”
#4: Bake at 350 F (176 C) for 45-50 minutes. In experimenting, I found that, at too high a temperature, the chickpeas burn quickly while being tender in the center. And if too low, no crisping seems to happen for a very long time. So 350 degrees is the sweet spot.