Preheat the oven to 350°F. Arrange the tostada shells on a baking sheet and lightly brush them with olive oil. Bake for about 5-7 minutes until they are crispy and golden.
In a medium bowl, combine the shredded rotisserie chicken with chili powder, cumin, salt, and pepper. Mix well to ensure the chicken is evenly coated with the spices.
Spread a generous layer of refried beans on each tostada shell.
Top the beans with the seasoned chicken mixture, followed by shredded lettuce, diced tomatoes, and shredded cheese.
Return the assembled tostadas to the oven for an additional 5-10 minutes, or until the cheese is melted and bubbly.
Remove from the oven and let cool slightly. Top each tostada with a dollop of sour cream, a spoonful of salsa, and slices of avocado.
Serve immediately and enjoy your delicious tostadas!