Browsing the local weekly ads, I noticed London Broil on sale. I know that it is both a method of cooking and a cut of meat and until I get to the store, I won’t know exactly where it is from (top round appears to be the best from my search).
Can I sliced that into strips or cubes and stir fry it with onions and peppers?
It will be tough if you aren’t careful - London broil is normally served rare and sliced thin, because it is rather a tough cut. You could marinate the hell out of it using something acidic, and make sure you slice it thin for cooking. Cubes or any chunk wider than 1/4", IMHO, would be almost inedible after being cooked well done in stir fry.
I think you’d be better off cooking it the traditional way and just serving it with onions and peppers. But that’s me.
Top round should be fine. It will be reasonably tender if cooked fast. Make julienne strips, not cubes. It will take no time at all to cook, don’t overdo it. Unless the oil is very hot it may not really brown, just darken from cooking. But all sorts of cuts are sold as London Broil, so you don’t know what you’ll get until you see it.