Cook lentils in a pot until tender using a 4:1 water to lentils ratio. Bring to boil, reduce to simmer and cook for about 30 minutes on low.
Meanwhile, dice sweet potato, spray with cooking spray and sprinkle with cinnamon, salt and pepper, and bake cubes at 400* for about 30 minutes.
Chop dates and toast walnuts in the microwave (1 minute on high) or in a dry skillet.
Combine mustard, vinegar and maple in a jar and shake to combine.
When lentils and potato are done, toss everything together and serve over chopped baby spinach.