Preheat oven to 400 degrees. Break the cauliflower into small florets and toss with a glug of olive oil and a hearty pinch of salt. Sprinkle with chili flakes if desired. Roast in the oven until crispy and tender, about 25-30 minutes.
While the cauliflower is roasting, cook the lentils. Rinse black lentils and transfer to a small saucepan. Cover with water and cook on medium until lentils are tender, about 20 minutes. Drain, rinse and set aside.
If you are using medjool dates and they are hard, soften them in warm water for 5 minutes. Coarsely chop.
Assemble the salad. Layer black lentils with roasted cauliflower on top. Sprinkle with thinly sliced red onion, feta crumbles, finely chopped fresh herbs, medjool date and a sprinkle of salt and pepper. Add a splash of white balsamic vinegar and taste for more salt. Enjoy warm or room temp.