Heat a large skillet over medium-high heat and add the oil. When the oil is hot, add the ground beef, season with 1/2 teaspoon salt and several grinds of black pepper and cook, crumbling it with a wooden spoon, until browned, about 6 minutes.
Reduce the heat to medium and add the onion and bell peppers. Cook until the vegetables begin to soften, about 5 minutes. Sprinkle with the chili powder and garlic and stir to incorporate. Add the tomatoes, beans with their liquid, corn and broth. Increase the heat to bring to a rapid simmer and cook until thickened, about 3 minutes.
Pour the mixture into a 9-by-13-inch baking dish. Top with the fries. Bake until the fries are browned and crisp, 30 to 35 minutes. Sprinkle with the Cheddar and bake until the cheese is bubbly, 5 to 7 minutes more. Serve topped with scallions and sour cream.