Combine soy sauce, lime juice, chili powder, and oil. If grilling, save a couple of tbs aside to toss with the vegetables.

Slice the meat into about 1/2 inch slices. If using skirt stake, flank steak or other meat with an obvious grain (lines through the meat), be sure to cut perpendicular to the grain, or you will be chewing a very long time. (Think about it - you want to create a lot of short fibers, not a few long ones)

If cooking in a skillet, marinate everything together in a bowl or plastic bag ( a zip-type works well ) If grilling marinate the meat and veggies separately. Even a few minutes helps, up to 2 hours is great.

If grilling, remove from marinade and grill.

For cooking in a skillet (preferable regular, not nonstick ), cook the meat first ( it will probably take two batches, depending upon your pan ) Add a little oil to the skillet and get it very hot ( the oil will shimmer ). If you don't get it hot enough ( or crowd too much meat in ) the meat will steam instead of browning. When the meat is browned, remove and add veggies. When they begin to soften, return meat to skillet to heat through.

Serve with salsa, sour cream, cilantro ( if desired ) and guacamole. If low-cab tortillas are availalble, that is a nice addition, but a fork works fine.