Preheat grill or cast iron skillet. Mix together the dry rub and rub it into the steak. Grill steak until your desired wellness (if on a grill, first place on high on direct heat, flip once, then move it to indirect heat until done). Set aside and let cool before slicing (against the grain!)
In a pan on medium heat, saute the onion, garlic, until golden. Add the optional chard and saute until wilted.
Next, make the chimichurri sauce by combining all ingredients in a food processor and blending until smooth.
Finally, mix together the salad ingredients with the onions/chard, then the steak slices, and top with chimichurri sauce.
Notes
Note that the rainbow chard is optional if you can't find it in the store. We just happened to have some from our garden.