Prepare the guacamole: In a medium bowl, mash the avocado until smooth. Mix in the diced tomato, red onion, cilantro, lime juice, garlic powder, salt, and pepper. Adjust seasoning to taste and set aside.

Warm the refried beans in a small saucepan over low heat, stirring occasionally until heated through.

If desired, lightly warm the tostada shells by brushing them with olive oil and placing them on a baking sheet in a preheated oven at 350°F (175°C) for 3-5 minutes. Remove and let cool slightly.

Assemble the tostadas: Spread a thin layer of refried beans onto each tostada shell.

Top the beans with shredded chicken, followed by a generous scoop of guacamole.

Add shredded lettuce and sprinkle cheddar cheese over each tostada.

If desired, drizzle with sour cream for extra flavor.

Serve immediately and enjoy!