Preheat the oven to 400°F. Place tostada shells on a baking sheet and bake for 5-7 minutes until crispy.
In a medium bowl, combine the shredded chicken, chili powder, cumin, salt, and pepper. Mix well to ensure the chicken is evenly coated with spices.
Spread a layer of refried beans on each tostada shell.
Top the beans with the seasoned shredded chicken.
Add shredded lettuce and diced tomatoes on top of the chicken.
Sprinkle shredded cheddar cheese over the toppings.
Add a dollop of sour cream on each tostada and garnish with fresh cilantro and avocado slices.
Serve immediately and enjoy!