In a large bowl, add corn, mayonnaise, red onion, cilantro, lime juice, salt and 2 tablespoons of cotija cheese.
Mix together with a spoon until the corn is evenly coated with all the ingredients. Set aside.
To assemble, spread about 3 to 4 tablespoons of refried beans onto each tostada and top with a scoop or two of the street corn mixture.
Sprinkle with some cotija cheese and a dash of chili powder. Eat up!