Passing a Function (with parameters) as a parameter?

It sounds like you want a Func<T>:

T GetCachedValue<T>(string key, Func<T> method) {
     T value;
     if(!cache.TryGetValue(key, out value)) {
         value = method();
         cache[key] = value;
     }
     return value;
}

The caller can then wrap this in many ways; for simple functions:

int i = GetCachedValue("Foo", GetNextValue);
...
int GetNextValue() {...}

or where arguments are involved, a closure:

var bar = ...
int i = GetCachedValue("Foo", () => GetNextValue(bar));