Making cake and added oil at end instead of at the beginning
It's been a while since I've done it (mine were mostly with muffins, although I might've done it with some zucchini brownies this past spring), but I want to say it'll come out, but it might be different.
You'll have developed more gluten, as oil coating the flour prevents the water from getting to it as quickly.  And there's the extra beating to get it all in there.  So it probably won't come out as light as you were hoping.
But I find zucchini bread &amp; cake recipes to be highly variable anyway -- as how much liquid you squeeze out of it (and by extension, how finely you grate it), has a huge impact on the final result.