While radishes are roasting, make your tahini sauce. Add tahini, 2 tablespoons olive oil, about 1 teaspoon lemon zest, the juice of 1 lemon, garlic, parsley, mint, 1 teaspoon salt and ½ teaspoon black pepper to a medium bowl. Whisk together, until combined. Add in water, 1 tablespoon at a time, until desired consistency is reached.