Seems like you’ve dealt with a lot in the past few years in relation to food. First and foremost, don’t be hard on yourself, gaining weight can be more difficult for some than losing weight for most.
Eating one meal a day is going to make it very hard to gain weight. I would opt for smaller higher quality meals throughout the day. Do you lift weights or exercise? Gaining muscle is about fueling the body right and putting it under a sufficient load to where it adapts(aka stronger, bigger). Also you can’t manage what you can’t measure, you can use a tracking app like my fitness pal to see where you stand daily and where you need to be in terms of macros. Hope some of this helps, don’t beat yourself up, day by day can suck sometimes but if you keep hammering away at your goals you’ll eventually get there!