I usually cook London broil on the grilling plate in the oven. However, that doesn't mean I do the same thing every time. The temperatures I have used range from a low 225 ºF to a high 400 ºF.
The factor that determined this was mostly the thickness of the steak, but occasionally how long I wanted to wait for it.
We return to our 2 rules of thumb:
Three steaks cooked at different temperatures:
Pic1: 225 ºF, no striping, evenly pink inside - 2016-10-31
All sessions were targeted for rare to medium rare.
None of these steaks were seared before or after the oven session.
The method that was used was the same each time, except for the temperature and cooking times:
That would suggest that the 225 ºF session was a thicker steak that required longer cooking, and the 400 ºF a thinner one that could be pushed faster. Look again.
Three steaks cooked at the same temperature:
Pic4: 350 ºF - 2019-05-02
The three steaks at 350 ºF are very similar in thickness. What you see here is that shorter cooking times leave a larger pink-to-red area in the center, and that decreases with longer cooking times until it would completely disappear and the steal would be well-done throughout. Not my favorite.
350 ºF is a good middle range for low to middle-thickness London broil, and doneness can be adjusted by adjusting the cooking time. However, the thicker cuts will be overdone on the outside while still raw in the center. Unlike in a frying pan, turning the piece will not really alleviate that because in the oven, the heat comes from both sides.