Preheat the oven to 400°F (200°C).
Place 1 teaspoon Crisco in the cast iron skillet and heat in the oven until melted.
In a large bowl, combine flour, cornmeal, egg, oil, and buttermilk. Stir until just mixed.
Add drained Mexi-corn, onion, green pepper, shredded cheese, and red pepper flakes. Mix gently.
Carefully pour the batter into the hot skillet over the melted Crisco.
Bake for 30–35 minutes, or until golden brown and a toothpick inserted in the center comes out clean.
Allow the cornbread to rest for 5–10 minutes before slicing.