Brush each tostada with olive oil
Cook tostadas for 3-4 minutes on each side in a 400-degree oven
Season the chicken breasts with the cumin, chili powder, garlic powder, salt & pepper.
Warm the chicken in a skillet over medium heat.
Shred the cooked chicken with two forks.
In a small saucepan, heat the refried beans over medium heat until warmed through.
Spread a layer of refried beans on each tostada shell.
Top with a portion of the shredded chicken.
Add shredded lettuce, diced tomatoes, and shredded cheese on top of the chicken.
Add a slice of avocado to each tostada.
Arrange the tostadas on a serving platter.
Serve with salsa on the side if desired.