In a pot add the Boneless, Skinless Chicken Breast (2 pound), Dried Oregano (1 teaspoon), Onion (1/2), Garlic (1 clove), Chicken Bouillon Powder (2 teaspoon) and Water (2 cup) to poach the chicken. Stir everything together. Bring to a boil, bring heat to low, cover and poach for 30 minutes or until the chicken is fully cooked. Then shredded it with 2 forks or your fingers.
For the sauce, in a blender add Plum Tomato (5), Garlic (2 clove), Chipotle Peppers in Adobo Sauce (2), Chicken Broth (1/2 cup) and Salt (to taste). Blend together and set aside.
In a large pot over medium heat, add the Cooking Oil (2 tablespoon) and cook the Yellow Onion (1) for about 5 minutes until they softened. Add the tomato sauce, then mix and simmer for 7-10 minutes until it thickens a little.
Add shredded chicken and stir to combine. Cook for 2-3 minutes.
Serve on top of a Tostada Shell (1 package) and top with Lettuce (to taste), Tomato (to taste), Sour Cream (to taste), Queso Fresco (to taste) and Avocado (to taste).