Preheat a grill pan or large cast-iron skillet over medium-high heat. Meanwhile, in a large saucepan, melt the butter over medium heat. Add the orzo and cook, stirring, until toasted and golden-brown, about 3 minutes. Stir in the chicken stock, rice, pimientos, chili powder and paprika and bring to a boil. Lower the heat, cover and simmer for 18 minutes. Remove from the heat and fluff with a fork.
While the pilaf is working, using a food processor, pulse the vinegar, shallot, garlic, parsley, thyme, marjoram and lemon peel until finely chopped, scraping down the food processor occasionally. Transfer the mixture to a bowl and stir in the EVOO; season with salt and pepper.
Season the steaks with salt and pepper. Cook on the grill pan, turning once, for 8 minutes for rare. Let the meat rest for a few minutes, then serve with the pilaf and chimichurri.