First, preheat your oven to 400°F (200°C). While it's heating, grab a baking sheet. Toss the chopped zucchini, quartered mushrooms, and diced eggplant in a bowl with olive oil, garlic powder, and a sprinkle of salt and pepper. Spread the vegetables in a single layer on the baking sheet. Roast them for about 25 minutes, or until they're tender and slightly caramelized. This step really brings out their natural sweetness.

In a large mixing bowl, combine the ricotta cheese, beaten egg, half of the shredded mozzarella, and half of the grated Parmesan. Stir in the roasted vegetables and fresh basil. It’s a colorful, creamy mixture that’s bursting with flavor. I like to taste it here—adjust the salt and pepper if necessary. You may be tempted to eat it straight from the bowl!

Next, fill the manicotti shells. I find that using a small spoon makes this job easier. You want to pack the filling carefully, but not too tightly—there's more room than it looks! Place each filled shell in a baking dish, standing upright if possible.

After all the shells are filled, pour the marinara sauce over the top. Use the remaining mozzarella and Parmesan to sprinkle generously over everything. This is where that melty goodness comes in! Cover the dish with foil and pop it in the oven.

Bake the manicotti for 25 minutes covered. Then, for the last 15 minutes, remove the foil. This allows the cheese on top to bubble and brown. You’ll want to keep an eye on it; nothing is worse than burnt cheese!

Once baked, remove the manicotti from the oven. Let it cool for about five minutes. Before serving, sprinkle a bit more fresh basil on top for that vibrant touch. Cut yourself a piece, and enjoy the beautiful harmony of flavors.