what can I feed my crab other than pellets

[Salem06]

At the moment I am feeding my red claw crab some algae wafers and shrimp pellets but it gets very messy to clean out of the tank, he doesnt mind it but I want to try leafy greens maybe green peas (frozen) or kale. im new to owning one and I have read that you can but I dont want to kill him so I thought I would try getting some answers on here any help would be appreciated