Verb for blowing up zombies

A word does come to mind that describes the act, but it's not strictly an English term, it is Military Slang and now often used in the gaming circles, with slight change in meaning.

Frag, Fragged will be the words corresponding to shoot and shot.

Google: "define frag"

verb /frag/ fragged, past participle; fragged, past tense; fragging, present participle; frags, 3rd person singular present

Deliberately kill (an unpopular senior officer), typically with a hand grenade

Smite ("To strike down or kill with godly force"; "To injure with divine power") might work, and it has the great past tense, smote. Thus: "I will smite you, zombie!" and "I smote the zombie!"

Also nuke (verb sense 3, "To completely destroy") and slag, which I've heard in sense of destroying something, although the wiktionary definition is "To talk badly about someone; to denigrate someone". Also, tchrist's blast suggestion is good; see sense 2, "To shatter, as if by an explosion".

The closest one-word answer I can come up with is detonate. That certainly blows things up. However, people are unlikely to themselves be explosive devices.

Perhaps you might try blast.

Based on your context, I like splat:

a sound made by splattering or slapping.

I like it even more in light of the definition of splatter:

to splash and scatter upon impact: The paint splattered when I dropped the bucket.

I think if you blew up a zombie, it would splatter.