TBH...I'd not give much of it at all. It might be too much particularly if it's the only food given. Maybe a tiny bit, chopped finely. Also...rinse it first to remove salt which can be quite dangerous in large amounts. Have you any tinned fish...sardines? That would be far better.
Does the cat look thin? What does a 'homeless' cat look like. Cats have a wonderful trick of pretending 'no one loves them' to get food, even if they have a lovely home.
Buy some cheap cat food in pouches and see if it eats that -don't buy chicken! it will think its well landed on its feet and you'll never see the back of it!
What does a homeless cat look like? Dishevelled, unshaven, maybe a few battle scars on it's face, usually has a dog by it's side (said dog may have a handkerchief tied around it's neck), a receptacle for collecting money. Those are the things i'd be looking for.