In a medium saucepan, bring water to a boil over high heat. Add lentils, reduce heat and simmer for about 30 minutes or until tender but not mushy. Drain and let cool to room temperature.

While lentils cook, preheat oven to 400°F. Lightly spray a large rimmed baking sheet with cooking spray; arrange sweet potatoes in a single layer on prepared baking sheet. Lightly spray with cooking spray and sprinkle with salt. Gently toss to coat. Roast in preheated oven for 20 to 25 minutes or until golden brown and tender. Let cool to room temperature in pan.

In a covered jar, combine olive oil, lemon juice, maple syrup and mustard. Seal and vigorously shake to combine. Season to taste with salt and pepper.

In a large bowl, gently toss together the spinach, optional dill, lentils, sweet potatoes and dressing.