I mean, it depends on how lean you’re talking about. A 6-foot guy can weigh 240, of course. But weighing 240 with really good ab definition as a natty? Unlikely.
This is a recurring topic for plenty of reasons. Most recently discussed at length in this thread: Natural Bodybuilding Stats and Gains
That sounds like a tiny breakfast. Maybe 500-ish calories and around 30g of protein. You’ve already put on size, so you know how to eat. Though a big part of that was from simply being so underweight beforehand, so I wouldn’t expect (or seek) the same rate of progress from here on out.
If you say the progress has been mostly muscle, that’s even better. Just don’t fall into the trap of seeking “many calories” instead of “many calories with ample quality protein to ensure muscle growth and minimize fat gain.”
Good call on using intra and post-workout nutrition. That’s a good time to throw down fast-absorbed protein and carbs.