Declare type of a object key

I have a XInterface like so:

export interface XInterface {
    foo: (() => Foo[]) | Foo[],
    bar: string,
    baz: number
}

Then, using the interface to declare an object I would like to the type of foo to be Foo[], like

const myObj: XInterface = {
    [myFoo1, myFoo2],
    'bar',
    1
}

but as I am already using the : to declare my array of Foo, I don't know how to ensure that foo is an array, not a function that returns an array.

How can I achieve that?