Preheat the broiler. Put the poblanos on a baking sheet and broil, turning, until charred, 3 to 5 minutes. Transfer to a bowl and cover; let cool slightly, then peel off the charred skins. Cut into 1-inch-thick strips; set aside.
Preheat the oven to 350 degrees F. Melt 2 tablespoons butter in a medium heavy saucepan over medium heat. Add almost two-thirds of the minced garlic and saute for 1 minute. Mix in the corn and saute for 5 minutes. Stir in the heavy cream and thyme. Cook over medium-low heat for 5 minutes for the flavors to incorporate. Turn off the heat and let cool slightly. Transfer to a blender and puree until smooth. Season with salt and pepper.
Heat the remaining 2 tablespoons butter in a small heavy skillet over medium heat. Add the onion and saute until translucent, about 5 minutes. Add the remaining minced garlic and cook for 1 minute. Mix in the zucchini and poblano strips and cook for 5 minutes to blend the flavors. Season with salt and pepper.
Spread about one-quarter of the corn sauce in a 9-by-13-inch flameproof baking dish. Cover with a layer of 3 lasagna noodles. Spread one-quarter of the poblano mixture and one-quarter of the cheese over the pasta. Repeat the layering three more times, ending with vegetables and cheese on top. Bake until browned and the noodles are cooked, about 50 minutes. Switch the oven to broil. Broil the lasagna until golden brown and bubbling, 8 to 10 minutes. Let stand 15 minutes before serving.