The big thing is getting enough protein to build up all of that muscle, most people don't get anywhere near the amount of protein they need. You should be eating about 100g of protein a day as a man if you're trying to build muscle, a typical burger is about 7g (and is rather horrible for you)...getting 100g without eating a billion calories can be tricky if you're not into certain foods. Body management is about 85% diet and 15% work, you can work out all you want, if you're not eating right most of that work is wasted. Expect to gain some fat, you should be eating more than you need while building muscle (your body won't build muscle if it doesn't feel it has the resources to safely do so.)
100g of protein a day is a rather small amount to get, really. And I'm not so sure about your 7g thing. A plain McDonald's hamburger has 12, while their regular cheeseburger has 15. And that's before you get into their larger offerings(which, let's be honest, when was the last time you ordered regular cheeseburger?). A Big Mac has 25g, an Angus Bacon and Cheese has 45g and a Double quarter pounder has 48g! Not arguing that they're bad for you, just saying I don't quite see your 7g thing.
With options like 3oz trimmed top sirloin having 25g(which means more than half that 100g in a single 8oz steak
), a 4oz chicken breast has 27g. 2 large eggs have a combined 12g. Really, it's not at all difficult to hit the 100g you've mentioned, even vegetarians should have little trouble hitting that.
That said, 100g is also not a set rule. Numerous sources I've read suggest it's more like .7g-1g(with the high end being far too much for most folks) per pound of desired body weight while keeping it at approximately a static percentage of your daily food intake(between 25-35% according to the live strong website). Even then, it really shouldn't be too bad(only 144g/day if we assume .8g/lb with a desired weight after training of 180 lbs with a total diet of 2304 calories/day at 25%).