Adjust an oven rack to the middle position and heat the oven to 475 degrees. Toss the tomatoes, onion, garlic, oil, and salt together on a foil-lined rimmed baking sheet and roast until the vegetables begin to brown darkly at the edges, 35 to 40 minutes, stirring once or twice for even coloring.

Reduce the oven temperature to 375 degrees. Transfer the roasted vegetables and any accumulated juices to a blender along with the chipotle, chili powder, lime juice, and reserved tomato juice. Puree for 8 to 10 seconds until the mixture is slightly chunky, then season with salt and pepper to taste.

In a 13 by 9-inch baking dish, combine the sauce, black beans, pinto beans, corn, zucchini, cilantro, and oregano. Spread the mixture into an even layer and top evenly with the cheese.

Bring the water to a boil in a large heavy-bottomed saucepan over high heat. Add salt, then slowly pour in the cornmeal while whisking vigorously to prevent lumps from forming. Reduce the heat to medium-high and cook for about 3 minutes, whisking constantly, until the cornmeal softens and the mixture thickens.

Off the heat, season the cornmeal with salt and pepper, then spread the warm mixture evenly over the filling with a rubber spatula, pushing it all the way to the edges of the baking dish.

Cover the dish with foil and bake for 30 minutes. Remove the foil and continue to bake for 30 to 35 minutes until the crust is beginning to brown and the filling is bubbling. Let the pie rest for 10 minutes before serving to allow the layers to set.