In a medium saucepan place 2 boneless skinless chicken breast in the pan and cover with water. Bring to a boil (about 20 minutes). Once the chicken is cooked and soft remove from pan, and carefully shred. Dump the water from the saucepan.
In the same saucepan as you boiled the chicken, combine chicken broth, enchilada sauce, and diced onion. Bring to a boil, and reduce heat to low and let it simmer for about 10-15 minutes. Stir in shredded cooked chicken and mix well. Then add 1/4 cup of shredded mexican blend cheese.
Heat refried beans in a saucepan over low heat until they stir easily.
Preheat oil in a large skillet on medium.
Right before you are about to assemble the chimichangas heat tortillas in a damp paper towel in the microwave for 30 seconds. Carefully remove one hot tortilla and begin spooning equal amounts of refried beans onto each tortillas followed by equal amounts of the chicken mixture, followed by shredded Mexican cheese (however much you desire). Roll up the tortillas, making sure no filling is exposed. *I found that these were super easy to roll when the tortilla was very hot--making the tortilla flexible and easy to work with!
Carefully place the the filled tortillas (one-by-one) in the frying pan seam side down *I used a large spatula to place them in the pan , turning once, until browned on both sides. Drain on paper towels. Serve immediately; top with guacamole and sour cream if desired.