Sauté minced garlic in hot olive oil in a large skillet over medium heat 1 minute.
Stir in eggplant and next 3 ingredients; cook, stirring occasionally, 15 to 20 minutes or until vegetables are tender and liquid evaporates. Stir in salt, Italian seasoning, and pepper; add diced tomatoes, and remove mixture from heat.
Spoon half of vegetable mixture in bottom of a lightly greased 13- x 9-inch baking dish. Layer evenly with stuffed frozen manicotti, grated Parmesan cheese, and half of mozzarella cheese; top with remaining half of vegetable mixture.
Bake at 375°, uncovered, for 40 minutes. Sprinkle evenly with remaining half of mozzarella cheese, and bake 10 more minutes or until cheese is melted and bubbly. Let stand 10 minutes before serving.