Preheat the oven to 375 F. Trim off the end and the green part of the leek, and thinly slice the remaining white part. Rinse and dry well.
On a large, parchment lined baking sheet, spread the leek, asparagus and fennel. Drizzle with ½ tbsp of olive oil, and season with salt and pepper. Roast in the oven for 20 minutes, or until veggies are tender crisp.
Meanwhile, combine the mustard, honey, lemon juice, olive oil and shallot in a blender or food processor. Add a good pinch of salt and a grind of pepper. Blend until smooth.
Using a sharp knife and a large cutting board, peel and segment the grapefruit. Cut the avocados in half and remove the pit. With a spoon, scoop the flesh out in one piece for each half and then slice.
When the veggies are finished, arrange them on a platter. Drizzle with the dressing, and top with the grapefruit, avocado, parmesan and mint. Serve immediately!
