Adjust the oven rack to the middle position and heat the oven to 475 degrees. Toss the tomatoes, onion, garlic, oil, and salt in a bowl, then spread them onto a rimmed baking sheet lined with aluminum foil. Roast until the vegetables begin to brown darkly at the edges, 35 to 40 minutes, stirring halfway through.

Remove the vegetables from the oven and reduce the temperature to 375 degrees. Transfer the roasted vegetables and any accumulated juices to a blender. Add the chipotle, chili powder, lime juice, and reserved tomato juice, then puree until the mixture is slightly chunky, about 8 to 10 seconds. Season the sauce with salt and pepper to taste.

Combine the blended sauce, black beans, pinto beans, corn, zucchini, cilantro, and oregano in a 13 by 9-inch baking dish and stir until well mixed. Spread the mixture into an even layer and top evenly with the cheese.

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

Remove the cornmeal from the heat and season with salt and pepper. Spread the warm cornmeal mixture evenly over the bean filling using a rubber spatula, pushing it all the way to the edges of the baking dish to create a seal.

Cover the dish with foil and bake for 30 minutes. Remove the foil and continue to bake until the crust is beginning to brown and the filling is bubbling, 30 to 35 minutes.

Let the pie cool for 10 minutes before serving—this allows the filling to set so it can be easily scooped.