Trim off the stem ends of the zucchini. Using a spoon, scoop out the flesh of the zucchini, leaving about ½" rim to create "boats". Place in the casserole dish, and lightly spray the tops with olive oil.
Spoon the mixture into the zucchini boats. Drizzle the remaining sauce over the stuffed zucchinis. Bake, uncovered, for 20 minutes. Top with mozzarella cheese. Bake for 5 more minutes, until the cheese is melted.