Preheat the oven to 400 degrees F. Cut up the cauliflower, removing the core and leaves. Cut the remaining cauliflower into small florets.
Place cauliflower in a bowl and toss with olive oil, salt, and pepper. Spread on a baking sheet. Roast in the oven for 20-25 minutes, stirring halfway through.
While cauliflower cooks, chop the dates into small pieces.
When cauliflower is several minutes from being done, make your sauce. Add the harissa, tahini, water, honey, and garlic powder to a small skillet. Heat over low heat and stir or whisk to combine. Heat for 3-5 minutes, stirring occasionally, until sauce is warm and ingredients are combined.
Plate the cauliflower and squeeze fresh lemon juice over the top. Add dates, then drizzle the harissa sauce over the cauliflower. Top with parsley or any other fresh herbs.