Preheat oven to 425°. In a roasting pan, toss cauliflower and shallots with 3 tbsp. oil and 3/4 tsp. salt. Roast, stirring occasionally, until light golden, about 20 minutes. Add chard stems and ribs, toss to coat, and roast until vegetables are very tender, 7 to 10 minutes more.
Stir in chard leaves, chickpeas, dukkah, and remaining 2 tbsp. oil. Roast until chard is wilted and tender, about 8 minutes. Stir; season to taste with more salt and dukkah.