Heat your oven to 425. In a large bowl, toss cauliflower with olive oil, garlic and onion powder and salt. Shake the bowl or stir well. Then add panko bread crumbs and stir or shake again. Pour cauliflower into sheet pan and roast for about 25 minutes, stirring 2-3 times while cooking.
In a small bowl, whisk together the tahini sauce ingredients. Taste and adjust seasoning. Add more water if too thick. When cauliflower is done, gently toss with the dressing and sprinkle with chopped mint before serving.