Add water and chicken breasts to a crockpot with ½ of an onion, 2 garlic cloves, and a pinch of salt. Turn the crockpot on to a simmer.
2. Step
While chicken is cooking, in a blender, blend ½ onion, tomatoes, 2 garlic cloves, salt, chipotles, and water. Once finished, in a skillet over medium heat, saute julienned onions until transparent.
3. Step
Once cooked, add chicken and sauce and cook for 15 minutes to combine.
4. Step
Lay a tostada shell on a flat surface, top with chicken mixture and desired toppings/garnishes. Repeat with remaining tostada shells.
