1. In a cast-iron pan over high heat, add the canola oil. When the oil shimmers, season both sides of the scallops with salt and pepper and add them to the pan. Sear, untouched, until a crust forms on the bottom of the scallops, 1 to 2 minutes. Using tongs, flip and repeat. Set aside to rest.
2. On a serving plate, layer half the grapefruit, radishes, avocado, scallops, and radish leaves. Top with a drizzle of olive oil. Season with salt and pepper, if needed. Repeat on another plate.