Make chimichurri by combining all ingredients in a bowl. I like to add them to a mortar and pestle and give it a nice blend. Let everything sit together while you make the rest.
Using a sharp knife, thinly slice the sirloin steak. Season well with salt and pepper. Melt butter in a large skillet and add diced onion. Cook for about 3-4 min or until onion has started to soften. Crank the heat up and add steak. Season again with salt and pepper and cook stirring often for about 5-6 minutes until steak has browned. Move steak to one side of the pan. Reduce heat and add slices of American cheese.
Crack 2 eggs into the other side of the pan. Add chimichurri sauce overtop. Cook until eggs are desired cook level.
Toast bun and then add steak and cheese. Add eggs and drizzle with more sauce. Enjoy!