Season the Chicken. Start by seasoning the chicken breasts with garlic powder, onion powder, salt, and black pepper.
Cook the Chicken. Heat olive oil in a skillet over medium heat. Cook the chicken breasts until they are golden brown and cooked through, about 6-8 minutes per side.
Shred the Chicken. Once cooked, let the chicken rest for a few minutes before shredding it with two forks.
Prepare the Tostada Shells. If using pre-made tostada shells, warm them in the oven for a few minutes. If making homemade, fry corn tortillas in hot oil until crispy and golden brown.
Spread the Beans. Spread a layer of refried beans onto each tostada shell.
Add the Chicken. Top the beans with a generous amount of shredded chicken.
Layer the Toppings. Add shredded lettuce, diced tomatoes, avocado slices, and shredded cheese.
Finish with Sauces. Drizzle sour cream over the top and sprinkle with fresh cilantro.