1. Preheat oven to 200°C. Line a rimmed baking sheet with foil. Toss potatoes and cauliflower with 3 Tbsp. oil on prepared sheet. Spread in an even layer and roast, tossing once halfway through, until cauliflower and potatoes are browned and slightly crisped, about 30 minutes. Let cool.
2. Meanwhile, heat remaining 2 Tbsp. oil in a large skillet over medium-high until it begins to shimmer. Add cumin and cook, stirring frequently, until they turn a medium shade of brown, about 1 minute. Reduce heat to medium and swirl in turmeric. Add onion and cook, stirring frequently, until translucent, 4–6 minutes. Add ginger, asafetida (if using), and chili powder and cook, stirring, until heated through and well combined, about 1 minute longer.
3. Stir in roasted potatoes and cauliflower, including any charred bits from the foil, and gently mix (don’t overmix, or the cauliflower will fall apart). Add salt and cook, tossing occasionally, until potatoes and cauliflower are tender (but not soggy!), 5–6 minutes. Remove from heat and add lime juice. Taste and add more lime juice or salt, if needed.
4. Transfer potatoes and cauliflower to a platter. Top with cilantro.

Recipe sources [1]