Place cauliflower on a sheet pan and toss it with 2 tablespoons if the oil. Season with 1 teaspoon of the salt and 1/2 teaspoon of the pepper. Roast until the florets are tender and charred in places, about 20 minutes. Let cool for 10 minutes
In a large bowl, combine the roasted cauliflower, cherry tomatoes, chard leaves and stems, lentils, orzo, olives, parsley, dill, and mint. Add the lemon zest and juice, pepper flakes, and the remaining 4 tablespoons olive oil, 1 teaspoon salt, and 1/2 teaspoon pepper.
Fold to combine and serve at room temperature or chilled. The salad can be made a day in advance and will keep for up to 7 days covered and refrigerated.