I use this for the chimichurri, but adjust it slightly to my taste: https://cafedelites.com/authentic-chimichurri-uruguay-argentina/#recipe . I use less oil, add some fresh lemon juice, and prefer using fresh oregano instead of dried.
As for the cauliflower steaks, I don't really have or follow any recipe... Just cut it carefully into rather thick slices so it doesn't break, use your favourite seasoning/marinade, then roast it in the oven or fry it in the skillet, baste it in butter with herbs... I usually have it with sauteed mushrooms and roasted baby potatoes...