Cook quinoa according to package instructions. Set aside to cool.
Shred or chop leftover chicken from previous evening's meal. Toss into a large mixing bowl.
In a small bowl whisk together Dijon mustard, honey, salt, and pepper; pour over chicken.
Roughly chop spinach and add to chicken along with mandarin wedges, halved grape tomatoes, almonds, and cooled quinoa. Toss gently to combine and evenly coat. Serve immediately.