I just took a peek at my deceptively delicious cookbook (jessica seinfeld) and the recipes that she hides avocado in are all chocolatey. Chocolate muffins, pudding and fondue. If you want to recipes, let me know and I'll type them out. I don't really hide it because we all love it here, but maybe these ideas with help some.
I second the idea of trying guacamole with the kids. DS LOVES guac! Especially with some good tortilla chips. How about quesadillas? You can spread a thin layer of avocado on the tortillas, and cover with cheese, other veggies, and some sort of protein. I use avocado alot in wraps as well. Same idea, spread a layer on the tortilla and then add your other ingredients. Spring rolls with veggies, avocado and noodles wrapped up in rice paper are great too. I'm not sure if that would hide it enough...maybe if you lay down the other veggies first, put a slice of avocado and then your noodles. Blending them with fruit and putting in freeze pop molds?