Vadouvan Roasted Cauliflower with Harissa Chickpea Curry

Name: Vadouvan-Roasted Cauliflower with Harissa Chickpea Curry
Ingredients: 2 Fresno chiles, thinly sliced; ¼ cup Champagne vinegar; ¼ teaspoon sugar; 1½ teaspoons kosher salt, divided, plus more; 1 head of cauliflower, cut into small florets; ¼ cup olive oil; 2 tablespoons vadouvan or curry powder; 2 shallots, thinly sliced; ¾ cup vegetable oil, divided; 1 15.5-ounce can chickpeas, rinsed, patted dry; 1 medium onion, chopped; 1 1-inch piece ginger, peeled, finely grated; 1 garlic clove, finely grated; 1 teaspoon grated lemongrass; 2 teaspoons tomato paste; 1 teaspoon harissa paste; 1 13.5-ounce can unsweetened coconut milk; 1 tablespoon chopped cilantro stems, plus sprigs for serving; Steamed basmati rice (for serving)