The Great Cleric: 1

A salaryman collapsed from a gunshot wound. When he came to, he had been reincarnated in another world as a fifteen-year-old healer with a talent for Holy magic named Luciel. In order to survive in this new world, he first decides to build up his body and begins intensive and strict training. Enduring physical training and awful flavors, his masochistic zombie streak takes root in this, the first volume of The Great Cleric!!