Rinse zucchini and squash and pat dry with paper towels. Cut zucchini and squash diagonally into 1/4 inch thick slices. Cut pepper halves lengthwise into 1/4 thick strips. Finely chop ginger and garlic. Combine broth, cornstarch, and salt in a cup; stir until smooth.Heat the wok over medium high heat until hot. Drizzle oil into the wok and add butter; swirl to coat the bottom. Add ginger and stir fry 30 seconds. Add zucchini and squash and stir fry about 6 minutes or until crisp tender. Stir in pepper and garlic; stir fry 1 minute.Stir cornstarch mixture until smooth and add to vegetables Stir fry until sauce boils and thickens.Transfer to a serving platter.