Golden Crisp Mexican Corn Tostadas

Ingredients

• 1/4 cup finely chopped red onion
• 8 yellow or white corn tortillas
• 1/4 cup finely chopped cilantro
• 2 cloves garlic, minced
• 2 tablespoons mayonnaise
• 2 cups fresh corn kernels
• 2 cups canned refried beans
• 1 lime, juiced
• 2 ripe avocados
• 1 tsp chili powder