The Andalusian Inquisition

Needs Fate of Iberia: every county in the region on Mozarabism specifically. The wiki route: in 867, replace the Umayyad Sultan with a custom Andalusian Mozarabic ruler (learning education, opinion-friendly traits), surrender the starting wars, and settle in for a multi-generation conversion campaign - Theologian tree, a good realm priest, county by county. Keep the Struggle in its Opportunity phase as long as possible; conversion is easier there. And since Mozarabism is Christian, run it as an Iberian-heritage ruler and Reconquista completes with it - two birds, one very long stone.