It can't be done if you want to be 220 tops. If you fight 205 you walk at 220. If you fight at 185 you walk at 200. If you fight at 170 you walk at 185-190 and the such. I have had 2 fights at 145 and walk around 163 and enter the cage at 165 or so since weigh ins are the day prior. So for you I would recommend staying where you're at and cutting to 170 and fighting there. It really should be an easy cut just dieting down to 180 a few weeks out then cutting the final 8-10 lbs the day before weigh ins.

If boot camp put you at around 185lbs, then that's a better "fighting" weight. I'm not sure why you have this goal of competing at 205lbs, but any good coach would encourage you to say at 185, and maybe learn how to cut weight to get down to 170lbs. WW or MW seems like a better weight class for you, based on what you're saying. Trying to gain 30lbs of mostly muscle is not only going to take a LOT of time and dedication, but will probably alter your body in such a way that it'll be hard to not gas out.

If you only want to add muscle (which should be your goal) look up MaxOT. Take the supplement push with a grain of salt. But if you follow the program and use good protein and creatine you could go from 185 to 205 easily and not put on any fat.

eat, squat, deadlift

I currently walk around at about 185-190 and I'm 6'3". I just got out of bootcamp so I lost 15 pounds (mostly fat). Now I want to get back up to at MOST 220, without exceeding that because it violates height/weight standards for the USMC.

What do y'all think? Once I get back from combat training I plan on fighting competitively at 205. Is it just as simple as eating and working out a lot? Any cool tricks y'all know?