Step 1: Preheat your oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish.
Step 2: Prepare the tomato sauce. Heat olive oil in a large pot over medium heat. Add chopped onion and sauté until softened, about 5-7 minutes. Add minced garlic and cook for another minute until fragrant.
Step 3: Stir in crushed tomatoes, tomato sauce, vegetable broth, oregano, basil, and red pepper flakes (if using). Bring to a simmer, then reduce heat and let it gently simmer for 20-30 minutes, allowing the flavors to meld. Season with salt and pepper to taste.
Step 4: Assemble the lasagna. Spread a thin layer of tomato sauce on the bottom of the prepared baking dish. Arrange a layer of thinly sliced sweet potatoes over the sauce, slightly overlapping. Top with a sprinkle of feta cheese and a few walnuts.
Step 5: Add another layer of tomato sauce, followed by a layer of butternut squash slices, then more feta and walnuts. Repeat with a layer of carrots, sauce, feta, and walnuts. Continue layering the vegetables, sauce, feta, and walnuts until all ingredients are used, ending with a final layer of sauce.
Step 6: Cover the baking dish tightly with aluminum foil. Bake for 45 minutes. Remove the foil and bake for an additional 20-30 minutes, or until the vegetables are tender and the top is lightly golden brown and bubbly.
Step 7: While the lasagna bakes uncovered, prepare the cranberry-honey glaze. In a small saucepan, combine dried cranberries, honey, and 1 tbsp water. Heat over low heat for 3-5 minutes, stirring occasionally, until cranberries are softened and glaze is slightly thickened. You can lightly mash some cranberries for a thicker consistency.
Step 8: Drizzle the cranberry-honey glaze over the hot lasagna immediately after removing it from the oven. Garnish with fresh parsley or thyme, if desired.
Step 9: Let the lasagna rest for 10-15 minutes before slicing and serving. This allows the layers to set and makes for easier serving.