Preheat oven to 425º. In a large cast-iron skillet over medium-high heat, heat oil. Add onions and cook until softened, 3 minutes, then add garlic and cook until fragrant, 1 minute more. Season with salt and pepper.
Add ground beef and break up with a wooden spoon. Cook until no pink remains, 6 minutes. Drain fat from skillet and return to heat.
Add cayenne and flour and stir for 1 minute. Pour in broth, then bring to a boil and simmer for 2 minutes. Fold in 1 cup cheese, peas, and corn.
Transfer meat mixture to a 9"-x-13" baking dish. Top with remaining 1 cup cheese and scatter tater tots and bacon in a single layer over the beef filling. Bake until cheese is melted and tots are golden, 27 to 30 minutes.
Let rest for 2 to 3 minutes and garnish with scallions before serving.