Preheat a grill to medium-high heat. Add the corn and grill, turning onto all sides, until evenly browned, about 10 minutes. Set aside to cool slightly, then remove the kernels.
Put a cast-iron skillet on the grill and heat. Drizzle with some olive oil and add the onions. Cook until translucent, about 5 minutes. Add the poblano slices and season with salt and pepper. Add the corn kernels to the skillet, then add the cheese and mix to combine. Continue to cook until the cheese is melted, about 5 minutes. Serve with tortilla chips and/or plantain chips for dipping.
To char the chiles (or any fresh chile): Put the chiles over a gas flame or underneath the broiler and cook until they are blackened on all sides. Enclose them in a plastic bag and let stand for 10 minutes to steam, which will make them easier to peel.