The thing I love about tostadas is that they are like a crispy taco and can be layered with any of your favorite savory toppings. I stack mine high and then dig through the layers with another tostada or chips, eating my way to the bottom. My favorite part is that the tostada on the bottom is still crispy, but soft in some spots too.
In a large pan, heat 2 tablespoons of oil to medium heat, add the onions and cook for 4 to 5 minutes. While the onions are cooking, in the blender, combine the Roma tomatoes, chipotle pepper, serrano pepper, tomato paste, salt and pepper and blend until smooth; set aside.
Add the diced peppers and garlic to the onions, cook for 2 minutes. Add the shredded chicken, tomato sauce from blender, cumin and a pinch of salt and pepper. Cook for a good 20 minutes or more to reduce the sauce. Taste for salt.
Serve as-is, or as a filling for tacos, tostadas, burritos or over a salad. In the pic, I layered guacamole, romaine lettuce, chicken, more guacamole and a drizzle of chipotle dressing on a baked tostada.