Steak Tostadas with Radish Salad

BLEND mayo, peppers and cilantro in blender until smooth. Pour 1/4 cup mayo mixture over steak in large shallow dish; turn steak over to coat both sides. Refrigerate 30 min. to marinate.

HEAT grill to medium heat. Remove steak from marinade; discard marinade. Grill steak 3 min. on each side or until medium doneness (160°F). Meanwhile, squeeze juice from 1 lime half into small bowl. Add radishes and dressing; mix well.

CUT steak across the grain into thin slices; place on tostada shells. Top with remaining mayo and radish mixtures. Squeeze juice of remaining lime over tostadas.