Combine flour, cayenne pepper, cumin, coriander, salt, and cardamom in a small bowl. Dip each halved scallop into the flour mixture to coat; set aside.
Place daikon rounds on serving platter. Top each with shredded lettuce; set aside.
Heat a medium nonstick skillet over medium heat. Coat with olive-oil spray, add coated scallops, and sear until light golden brown and cooked through, about 1 minute per side. Transfer each seared scallop half to a daikon round. Serve warm or at room temperature.