In a large bowl, whisk together the masa harina and salt.
Gradually add the warm water, stirring until a dough forms.
Knead the dough for 2-3 minutes, until smooth.
Divide the dough into 6 equal pieces and roll each piece into a ball.
Flatten each ball into a disk, about 1/4-inch thick.
Heat a cast iron skillet or griddle over medium-high heat. Cook the gorditas for 2-3 minutes on each side, until lightly browned and cooked through.
In a large skillet, heat the olive oil over medium heat.
Add the onion, red bell pepper, and garlic. Cook for 3-4 minutes, until the vegetables are softened.
Add the cumin, smoked paprika, chili powder, salt, and pepper to the skillet and stir to combine.
Add the black beans and corn to the skillet and cook for an additional 2-3 minutes, until the filling is heated through.
Remove the skillet from heat and stir in the cilantro and lime juice.
Use a knife to cut a slit in the side of each gordita, creating a pocket. Spoon about 1/4 cup of filling into each gordita pocket.
Serve with vegan sour cream or salsa, if desired.