Preheat the oven to 200C / 400F. Cut the potatoes in half lengthwise if necessary so that they're all about the same size, then place onto a large baking sheet with the olive oil and salt. Mix to coat, then roast for 35-40 minutes, or until golden.
Wash and trim the asparagus. In the last 5 minutes of cooking time for the potatoes, just toss the asparagus in the oven with them. They should turn bright green and soften slightly.
Take the potatoes and asparagus out of the oven and place them into a large bowl. Add the greens and lentils, then top with the lemon vinaigrette and stir to combine. Serve warm.
Lemon Mustard Vinaigrette
Add all ingredients to a small jar or bowl and shake or whisk to combine.
Notes
* The chewiness of green lentils holds up well here, but brown or beluga lentils can be used instead. * The vinegar adds a little more acidity, which I prefer.