Place dried ancho and guajillo chilies on a microwave-safe plate and microwave until pliable and toasty-smelling, 10 to 20 seconds.
Transfer to the jar of a blender and add chipotle peppers, orange juice, lime juice, olive oil, soy sauce, fish sauce, garlic, cilantro, cumin, coriander, and brown sugar. Blend until a smooth sauce has formed, about 1 minute. Season to taste with salt.
Transfer half of the sauce to a large bowl and the other half to a sealed container. Set aside the sealed container in the refrigerator.
Add an extra 2 teaspoons of salt to the sauce in the bowl. It should taste slightly saltier than is comfortable to taste.
Add the steak, one at a time, to bowl and turn to completely coat in the sauce.
Transfer to a gallon size ziplock bag. Repeat with remaining steak, adding it all to the same bag. Pour any excess marinade over the steak. Squeeze all air out of the bag and seal. Refrigerate for at least 3 hours and up to overnight.
When ready to cook, remove the extra sauce from the fridge, and warm in a small pot over medium low heat.
If you are grilling the steak, turn on the gas grill, or light the charcoal. You can also cook this under the broiler in your oven, or in a large cast iron grill pan on the stove.
Remove steak from marinade and wipe off excess. Place directly over the hot side of the grill. If using a gas grill, cover; if using a charcoal grill, leave exposed.
Cook, turning occasionally, until steak is well charred on outside and center registers 110°F on an instant-read thermometer, 5 to 10 minutes total. If using the broiler, set your broiler to high, place the steaks on a broiler pan or large sheet pan and broil for about 5 minutes per side. If grilling in a pan, heat the pan on high heat, and grill the steaks for about 5-7 minutes per side.
Transfer to a cutting board and allow to rest for 5 minutes. Slice thinly against the grain.
I like to set up a burrito bar where people can assemble and build their own burritos. Set up the extra sauce, lime wedges, onion, cilantro, avocado, salsa, sour cream, cheese and tortillas on the side.
Feel free to make tacos instead of burritos – either way this is a crowd pleaser!