Couscous halloumi salad. Super fast to prepare, and easy to modify with any veggies on hand (onion, red pepper, broccoli), or substitute feta for halloumi. Short on time, no need to grill the cheese, just cube it and toss into the warm couscous to get a little melty while you prep the veg. Tasty on it's own - I've never even tried it with the dressing.
THAI CHICKEN NOODLE SOUP: Even if you don't have much chicken left over, you should still make this. A few shreds will be plenty. (And this recipe is worth bearing in mind even when your starting point is not leftover chicken: if you were to bung in some frozen prawns at the end, making sure you cook them through, this would make for a fabulous storecupboard supper.)