Mexican Street Corn Tostadas

Ingredients

• 1 15-ounce can whole kernel corn, (drained)
• 1/4 cup mayonnaise
• 1/4 cup finely chopped red onion
• 1/3 cup finely chopped cilantro
• Juice of half a lime
• 1/4 teaspoon salt
• 2 tablespoons cotija cheese, (plus more for topping)
• 1 15-ounce can refried beans
• 8 tostada shells, (store-bought or homemade)
• chili powder to season for topping, (optional)