In a bowl, mash the avocado with a fork. Mix in the cumin, lime juice, chili powder, salt and pepper.
Gently fold the cherry tomatoes, green onion, yellow pepper and coriander into the avocado. Adjust seasoning. Transfer to a reusable, sealed container, and pack for work along with the crackers and the egg.
At lunchtime, spoon some of the guacamole onto each cracker. Top each with a few sprigs of arugula or spinach and slices of egg.