In a 10-inch non-stick skillet heat oil over moderately high heat until hot but not smoking and saute pine nuts, stirring, until golden. With a slotted spoon transfer pine nuts to paper towels to drain.
In skillet cook garlic over moderate heat, stirring until golden and with slotted spoon discard. Add fennel to skillet and cook, stirring until golden, about 2 minutes. Add lemon juice and salt and pepper to taste and cook until fennel is crisp-tender. Stir in radicchio and saute mixture over moderately high heat, tossing with two wooden spoons, just until radicchio is wilted and tender. Add pine nuts and season with salt and pepper.