Reconquista

Every county in Iberia Christian, while you control the region as an Iberian-heritage Christian. The wiki route: in 867, replace the Umayyad Sultan with a custom Andalusian-culture Christian (learning education; Gregarious, Just and Temperate keep your Muslim vassals from hating you on sight). Surrender the starting wars, work the Theologian tree for cheap county conversion, and eat the independent Iberian counties before Asturias does - then the eastern islands, Navarra, and Asturias last. With Fate of Iberia installed, hold the Struggle in its Opportunity phase as long as you can (or start Mozarab to be auto-Involved and use Struggle CBs) - which also lines up The Andalusian Inquisition.