Pound chicken breast to even thickness (1/2"-3/4") using a meat mallet or rolling pan. Sprinkle chicken with taco seasoning and salt.
Heat oil and butter in a skillet over medium heat. Cook chicken for 3-4 minutes per side, or until internal temperature reaches 165 degrees. Remove from the heat.
While the chicken is cooking, wash and chop the vegetables.
Use two forks to shred the chicken, then return to the skillet. Add bouillon and water. Cook and stir over medium low heat until heated through.
For each tostada: Spread 2-3 tablespoons of refried beans on a tostada shell. Top with about 1/3 cup of shredded chicken, 2 tablespoons of cheese, 1/3 cup of lettuce, and a tablespoon or two of diced tomatoes.
Repeat with each tortilla shell. Serve immediately with additional garnishes on the side.
Notes
If your family loves refried beans, you may want to use 2 cans.