Put a baking sheet on the middle oven rack and preheat to 450 degrees F. Toss the cauliflower, red onion, 3 tablespoons olive oil, 1/2 teaspoon salt, the garlic and curry powder in a large bowl. Spread on the hot baking sheet and roast, without stirring, until very tender and well browned in spots, about 25 minutes.
Meanwhile, heat the remaining 2 tablespoons olive oil in a large nonstick skillet over high heat. Season the scallops with salt, add to the skillet and cook, undisturbed, until well browned on the bottom, about 3 minutes. Flip and cook until no longer translucent, about 1 more minute; transfer the scallops to a plate.
Toss the cauliflower mixture with the raisins and cashews and divide among plates. Top with the scallops and cilantro; drizzle with the yogurt. Serve with lime wedges.