For the Ranchero Sauce:

• Heat olive oil in a large skillet over medium-high heat. Add shallot, bell pepper, and jalapeno pepper, season with salt and pepper, then saute until vegetables are tender, 5 minutes. Add garlic, cumin, and cayenne pepper then saute for 1 more minute. Add chicken broth and crushed tomatoes then turn heat to high to bring liquid to a boil. Reduce heat slightly then boil, stirring often, until sauce reduces by half (3 cups,) about 20 minutes. (A splatter screen is very helpful, especially near the end.) Taste then add salt and pepper if necessary, and then stir in fresh cilantro.
• To a large, 6 quart crock pot add the chicken breasts, chicken broth, salt, pepper, red pepper flakes, lime juice, and 2 cups Ranchero Sauce. Cover then cook on low for 4 hours or until chicken shreds easily with two forks. Shred chicken then place back into the juices and cook on low for 1 more hour. Scoop chicken into a bowl then mix with remaining Ranchero Sauce. Use chicken as filling for tacos, enchiladas, nachos, or tostadas.