By using store bought tortillas or tostadas, you can save yourself some time but if you’re feeling up to a challenge then not why make your own? You’ll find a link to making your own tortillas in this recipe.
In a small bowl, stir together the chili powder, paprika, cumin, salt and pepper. Rub all over the chicken breasts. Place them in a parchment bag with the onion, sweet red pepper, lime juice, beer or chicken broth, and chipotle puree.
Fold the bag up to close and place on a baking sheet. Bake at 350°F (180°C) for 25-30 minutes, or until the chicken is no longer pink inside and the juices run clear. If you are using a meat thermometer, it should read 165°F (74°C) at the thickest part of the breast.
Remove the chicken breasts from the bag and set aside to cool.
In a food processor, blend together the black beans, garlic, lime juice, chili powder, cumin, oregano, oil, and cilantro. Add the water a bit at a time to loosen up the mixture. What you don't use, you can serve with tortilla chips as a dip.
If you really want to go all out and do everything home made, and I suggest you make your own tostadas. You will be happy you did. You can find the recipe for the no fail tortilla pitas here: http://www.chasingtomatoes.ca/2009/09/andreas-no-fail-tortilla-pitas.html. It makes 8, and for our family 1 tostada each is enough. You should have enough beans and chicken that combined with veggies will make about 6-8 tostadas (We go heavy on the veggies, though).
Serve the warm shredded chicken with the bean paste and an assortment of toppings. I smeared the pitas with bean paste, then heaped it with chicken, lettuce, sweet peppers, cheddar cheese, avocado, sliced fresh tomato, cilantro, and sour cream mixed with a little more chipotle.
You can buy chipotle peppers in cans in the Mexican food section at the store. I like the ones canned in adobo sauce but I never can use the whole thing. Instead, I puree the extra chipotles and portion them out into ice cube trays, and freeze them so that I can thaw and use them in the future. They add a lot of flavor to dishes.