Complex sentence: The chain had to contend with the rise of grilled chicken as Americans became increasingly health conscious, competing against the growing El Pollo Loco restaurant chain, and also with Burger King, which had just introduced the BK Broiler, a grilled chicken burger.
Split into simpler sentences: The chain had to contend with the rise of grilled chicken as Americans became increasingly health conscious. KFC found itself competing against the growing El Pollo Loco restaurant chain, as well as with Burger King, which had just introduced the BK Broiler, a grilled chicken burger.