Preheat the broiler. On a rimmed baking sheet, combine the cauliflower florets, poblano pepper, and scallions with the vegetable oil, chili powder, cumin, and 1/2 teaspoon kosher salt. Spread the mixture in an even layer and broil until the vegetables become browned around the edges, approximately 7 to 10 minutes.

In the meantime, prepare the biscuit mixture. In a medium bowl, whisk together the cornmeal, flour, baking powder, brown sugar, and 3/4 teaspoon salt. Use your fingertips to incorporate the butter into the cornmeal blend until the mixture resembles coarse crumbs. Using a fork, gently stir in the buttermilk and 1/3 cup of the cheese until the ingredients are just combined.

Once the vegetables have finished broiling, preheat the oven to 475°F. Carefully add the black beans with their liquid, tomato sauce, fire-roasted corn, vegetable broth, and 1/2 teaspoon salt to the baking sheet with the roasted vegetables. Stir gently to combine the ingredients.

Spoon the biscuit dough on top of the chili mixture in about 12 mounds, spaced roughly 1 1/2 inches apart. Sprinkle the remaining 1/3 cup of shredded cheese over the biscuits. Bake until the chili bubbles and the biscuits are golden brown and fully cooked, about 25 to 30 minutes. Garnish with chopped scallions and serve hot.