In a food processor, blend yellow onion, garlic cloves, chipotle peppers, adobo sauce, ancho chili powder, cumin, oregano, salt, and black pepper. Slowly add water until smooth.

Place the sirloin steaks in a zip-lock bag and pour the marinade over them. Seal the bag and refrigerate overnight.

30 minutes before cooking, let the steaks reach room temperature. Preheat your grill or skillet.

Cook the steaks on the skillet or grill for 6-8 minutes on each side until beautifully browned. Aim for 145°F for medium-rare.

Transfer the cooked steaks to a cutting board and cover loosely with foil. Let them rest for about 10 minutes.

After resting, slice the steak against the grain, garnish with cilantro, and serve with lime wedges or grilled veggies.