I think you could use cut up chunks of cooked chicken or beef in place of the mushrooms. It’s usually the texture of mushrooms that some people don’t like. If you want to retain the mushroomy flavor, without having the texture of the schrooms you could add some Dried Mushroom Powder
I’m thinking that some waterchestnuts might be a good substitution for the schrooms too. Or you could use Trader Joe’s Organic Baked Tofu which is not squishy at all and has a taste and texture that is very similar to chicken. I’ve used it in several creamy cold vegetable salads and my meat eating relatives like it. They thought it was either chicken or cheese chunks. I think it would be a perfect sub for schrooms, because it has that umami flavor without any squishiness.