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.

Heat up the refried beans in a glass dish in the microwave for about 2 to 3 minutes, or until fully heated through.

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.