Preheat oven to 450 degrees Fahrenheit.
Cut each zucchini in half lengthwise; scoop out pulp, leaving a 1/4-inch-thick shell. Reserve pulp for another use (risotto or pasta sauce). Arrange zucchini shells in a single layer in a baking dish coated with cooking spray.
Combine basil and the rest of the ingredients (excluding parsley), stirring well with a whisk. Divide mixture evenly among shells, pressing gently. Bake at 450 degrees for 20 minutes or until zucchini is tender. Garnish with parsley, if desired.