Preheat oven to 400°F and line a large baking sheet with parchment paper.
In a large mixing bowl, toss cauliflower florets with 1 tablespoon olive oil. Sprinkle with salt and pepper. Transfer to a prepared baking sheet and roast for 20 minutes, stirring halfway through.
In the same mixing bowl, toss mushrooms with remaining 1 tablespoon olive oil, add to cauliflower on the sheet pan, and stir. Continue roasting 10 more minutes, or until tender.
Add the dressing ingredients to a small bowl and whisk to combine.
Warm the cooked lentils in the microwave according to package instructions. Mix with the roasted mushrooms and cauliflower. Toss with balsamic dressing.
To serve, place arugula in serving dish, top with warm lentils and roasted vegetables. Garnish with pine nuts, parsley, and parmesan. Enjoy!