Heat a large skillet on medium high. When hot, add oil and the corn kernels. Season with 1 teaspoon of sea salt and a few turns of freshly ground black pepper. Cook for 10-12 minutes, leaving to cook for 2 minutes at a time and then tossing, until the corn is charred. Transfer to a large bowl.
Meanwhile, place half of the avocado into a medium bowl and mash it up with a fork. To the avocado, add the sour cream or crema, coriander/cilantro, garlic, lime juice, jalapeno, a big pinch of sea salt and some black pepper. Stir to combine. Taste to check that you are happy with the seasonings, adjusting lime, salt and pepper, if needed.
Cut the remaining avocado into cubes. Add this to the corn, along with the avocado crema and toss to combine. Taste and season with sea salt and black pepper. To serve, top the corn with cotija or feta cheese, scatter with chilli powder, cayenne or smoked paprika, along with the coriander/cilantro leaves. Serve with lime wedges on the side, along with your choice of tortillas or corn chips.