To roast jalapeño, turn boiler on high and place oven rack on top shelf. Place a piece of tinfoil on rack. Slice jalapeño in half lengthwise and remove seeds. Place jalapeño cut side down onto tinfoil. Broil until jalapeño skin starts to blacken (about 5 minutes or so - keep a close eye on them). Remove from oven and let cool. Once cool, remove skins and finely dice. Set aside.Heat a large skillet over medium high heat, add vegetable oil to coat bottom. When it is hot - it'll have slight ripples on the surface. Add corn and whole garlic clove and a pinch of salt. Cook corn until browning on one side and then toss. Continue to cook until corn is browned well and charred in spots- about 5 to 7 minutes. If corn begins to pop or darken too much, reduce heat.Once cooked, remove from heat and remove garlic clove. Stir in mayonnaise, green onions, jalapeño, and lime juice. Taste and season with salt to your liking.Evenly sprinkle chopped cilantro leaves, crumbled cotija cheese, and chili powder over corn.Serve warm. Store in sealed container in fridge. Reheats well the next day or eaten cold!