Preheat oven to 375 degrees Fahrenheit.
Make your tostada shells. Place tortillas in the oven directly on the racks. Bake for 10 minutes, flipping halfway through, until crispy and hard (they need to be crispy to hold the toppings). You can also place them on a baking sheet if desired, but right on the rack helps with even airflow. Just be careful when flipping and removing them.
When the tostadas start to cook, make your chicken mixture. Heat a large skillet over medium-low heat, add 1 tablespoon of oil, and let it get hot. Add onions and saute for 3-4 minutes until softened. Next, add your shredded chicken, salsa, diced green chiles, cumin, coriander, and salt and pepper. Saute for another 3-4 minutes until warmed through. Turn down the heat to the lowest setting to keep warm.
When the chicken starts to cook, heat your refried beans. Add your beans to a small saucepan and break them up. Cook for 5-6 minutes, until warmed through, making sure to stir frequently so they don’t stick.
Assemble your tostadas. Take one tortilla and spread a large heaping spoonful of refried beans on it and spread it out in a thin layer. Then take 1-2 spoonfuls of the shredded chicken and pile it on top of the beans. Top with shredded lettuce, pico de Gallo, avocado, and cheese. Repeat with remaining tortillas, evenly dividing the beans, meat, cheese, and toppings.
Enjoy! Top with more topping if desired and enjoy!