Prepare the vegetables: Heat olive oil in a large skillet over medium heat. Add chopped onion and sauté until softened, about 5 minutes. Add minced garlic, diced bell pepper, and zucchini, cooking for another 5-7 minutes until vegetables are tender-crisp. Set aside.

Make the green curry béchamel: In a separate saucepan, melt butter over medium heat. Whisk in flour and cook for 1 minute to create a roux. Gradually whisk in coconut milk and vegetable broth until smooth. Bring to a simmer, stirring constantly, until the sauce thickens.

Stir in the green curry paste, fish sauce (if using), and sugar into the béchamel. Cook for 2-3 minutes, allowing the flavors to meld. Stir in the chopped fresh basil. Season with salt and pepper to taste.

Preheat oven to 375°F (190°C).

Assemble the lasagna: Spread a thin layer of green curry béchamel on the bottom of a 9x13 inch baking dish. Layer with 3 lasagna noodles, followed by half of the sautéed vegetables, then another layer of béchamel, and sprinkle with half of the mozzarella and Parmesan cheese.

Repeat the layering: Add another 3 lasagna noodles, the remaining half of the sautéed vegetables, another layer of béchamel, and the rest of the mozzarella and Parmesan cheese.

Top with the final 3 lasagna noodles and the remaining béchamel sauce. You can lightly sprinkle with a little extra mozzarella if desired.

Bake for 30-35 minutes, or until bubbly and the cheese is golden brown. If the top browns too quickly, cover loosely with foil during the last 10-15 minutes.

Let the lasagna rest for 10 minutes before slicing and serving. This allows the layers to set properly.