NO doubt, it woudld be an unhealthy meal for a tropical fish. But of course 1 meal won't matter one bit , in the life of a fish.
##1) if you are ever going to feed COW to a fish it should be UNCOOKED. Have any fish ever evolved with cooked food in their diet?

C'mon, think about it.
Yes, cooking is a way to make food safer for human consumption, but no fish is known to benefit from 'germ free' but de-natured' altered protein (?).
#2)Even the leanest cuts of COW ( Liver, beef heart) are still at least 30% calories from fat. Food is measured in calories ( energy) and the leanest beef still has significant amounts of saturated fat. A very large portion of fat, even from leaner cuts ( trimmed beef heart, liver) is saturated fat that a cold blooded fish, more then likely, can not process, if fed often enough, in large amounts.
Lean gound beef : well over 50% calories from fat, with most of that fat saturated; something most fishes would never encounter in their natural diet. Most cuts of beef: well over 60 % calories from fat; mostly saturated fat that would not usually make up a significant part of an aquatic animal's diet. BUT of course for most ACTIVE humans, probably very good and nutricious.
Why feed cooked beef when you could feed chopped raw fish/ shrimp to your fish instead??