Make the Sauce: In a saucepan over medium heat, warm 1½ tsp olive oil.
Sauté the ½ cup finely chopped onion for 7 minutes until soft.
Stir in the minced garlic, sage, and oregano and cook for 30 seconds until fragrant.
Add the fire-roasted tomatoes and balsamic vinegar, season with salt and pepper, then cover and simmer on low for 10 minutes. For a smooth consistency, purée the sauce with an immersion blender.
Prepare the Filling: In a large skillet, heat 1 Tbs olive oil over medium heat.
Sauté the 1½ cups chopped onion for 10 minutes.
Add the diced zucchini and corn, increase heat to medium-high, and cook for 3-5 minutes until the veggies start to brown.
Stir in the minced garlic and sage, then remove from heat.
Mix in the ricotta, 2 Tbs Parmesan, and a pinch of nutmeg.
Season to taste.
Cook the Noodles: Bring a large pot of salted water to a boil.
Add the no-cook lasagna noodles and cook for just 3 minutes, until they are pliable but not fully cooked.
Drain and immediately transfer to a bowl of cold water to stop the cooking process.
Drain again, pat dry, and cut each noodle in half width-wise.
Assemble the Cannelloni: Preheat your oven to 350°F / 175°C.
Spread ½ cup of the tomato sauce on the bottom of a 9-inch square baking dish. Spoon about 3 Tbs of the zucchini-ricotta mixture down the center of each halved noodle.
Roll it up into a tube and place it seam-side down in the baking dish.
Repeat with all noodles and filling.
Bake to Perfection: Pour the remaining tomato sauce evenly over the cannelloni.
Sprinkle with the remaining 2 Tbs Parmesan and the optional mozzarella cheese.
Bake for 25 minutes, or until the sauce is bubbly and the cheese is melted and golden.
Don't overcook the lasagna noodles. They just need to be pliable enough to roll without breaking; they will finish cooking in the oven.
