Season the chicken. In a large mixing bowl, toss the chicken with olive oil, kosher salt, cumin, smoked paprika, and garlic powder until the chicken is thoroughly coated.
Brown the chicken. Set your Instant Pot to the saute function and let it heat up for a minute or so. Add 1 tablespoon of olive oil and let it heat up for 30 seconds. Add the seasoned chicken and brown on all sides.
Load the Instant Pot. Add the onion, chipotles, adobo sauce, chicken stock, enchilada sauce, oregano, and bay leaves.
Cook. Seal the Instant Pot and cook on high pressure for 15 minutes. Allow the pressure to naturally release.
Shred. Once the pressure has been released, shred the chicken with two forks inside the Instant Pot.
Rest. Allow the chicken to sit in the sauce for a few minutes to soak in the sauce.
For the Tostadas
Prep. Preheat the oven to 410°F and line baking sheets with parchment paper.
Bake. Brush each tortilla with olive oil and arrange them in a single layer on the prepared baking sheets. Bake for 10 minutes, flipping halfway through.
Assemble. Spread ¼ cup refried beans over each tostada followed by 2-3 tablespoons guacamole, a handful of the chicken mixture, a hearty pinch of shredded cabbage, and 2-3 tablespoons pico de galo. Serve.