Heat oil in a large non-stick skillet over high heat until shimmering. Add corn, season to taste with salt, and cook without moving until charred on one side, about 2 minutes. Toss corn, stir, and repeat until charred on second side, about 2 minutes longer. Transfer to a large bowl and clean skillet.
Add mayonnaise, cheese, cilantro, jalapeño, garlic, lime juice, and chili powder and toss to combine. Season with salt to taste.
Heat oil in the same skillet used for corn over medium-high heat. Add sliced chicken and sprinkle with taco seasoning. Stir to combine and sautee until fully cooked, about 5 minutes.
Top tortillas with Mexican street corn and chicken and sprinkle with chopped red onions, if desired. Serve immediately.