Thaw pastry according to package directions. Preheat oven to 375 degrees F. On a lightly floured surface, roll puff pastry sheet to a 14-inch square. Cut into 4 equal squares. Invert four 10-ounce casserole cups onto a large baking sheet; coat outsides of cups with nonstick cooking spray.
Drape pastry squares over inverted cups, pinching sides to fit around the cups.
Bake pastry squares for 20 minutes or until golden brown. Remove from oven and let cool for several minutes, then carefully pull the shells from the outsides of the casserole cups. Invert shells onto individual plates.
Coat a large nonstick skillet with nonstick cooking spray. Stir-fry garlic for 15 seconds, then add onion and stir-fry 1 minute more. Add the zucchini; cook for 2 to 3 minutes more or until vegetables are crisp-tender.
Remove the vegetables and add the beef to the skillet. Stir-fry for 3 to 4 minutes or until done. Return vegetables to the skillet. Add the gravy, marjoram or thyme, and pepper; cook and stir about 1 minute more or until heated through. Carefully spoon one fourth of the hot beef and vegetable mixture into each baked pastry shell. Makes 4 main-dish servings.