Tomatoes. 180 calories per kilo and tasty as fuck. You could eat a plateful every waking hour and still lose weight (while getting twice your recommended protein intake).
What he said. I've been living off of zucchini, either spiral slicing it into noodles or roasting it with other veggies and melting a little parm on it. Carrots are great, sugar snap peas for snacking, cauliflower, broccoli, really you can't go wrong and can eat a fuckton with minimal calories if you cook it right/eat it raw.