I had been asking myself this just the other week..!And of course I know what the answer is. We all know what the answer is, it’s just sound it consistently.
Bad habits increasing during lock-down, in terms of eating and lifestyle, knowing what I need to do - but why am I not doing it? So then, motivation hit...that I needed to really change things up. Like you, I wasn't eating enough during the day and not great choices if I did (although not junk food), and then leading to being really hungry in the evening and then not great choices as a result of that. While I've only just started switching up my mindset, so early days yet, for me it's in really noting what my motivation is and why. And then considering the psychological aspects of the bad habits - in order to do the opposite.
Small changes I've implemented so far - having the right food on hand. Berries and apples for example as a mid-morning snack. Even if I need to jump on a zoom meeting around that time, I will snack on them instead of just waiting and skipping that meal. Foods on hand, for me is the key, along with the motivation and mindset to change. Boiled eggs, salads I can easily put together, vegetables and protein. It could even be having tuna with veggies that are microwaved while you're at work. Take a couple of carrots and boiled eggs with you - and that's quick prep during your 30mins lunch. Dinner could be wrapping salmon in foil into the oven for 15 mins and just adding some veggies as a side. Basically as others have suggested though, preparing the food. Or even, in my case, just having it on hand and preparing on the go.
I'm currently cutting out caffeine and alcohol and eating protein with every meal (which is filling), then snacking on berries, yoghurt, veggies in between. In a short period of time eating this way, I've dropped 7lbs. I'm average in size, but my clothes were getting snug and I wasn't feeling as good as I know I can. The other night, I was craving red wine and popcorn while we watched a show. I mentally reminded myself it was just a habit I'd gotten into and asked myself if that choice would get me to where I wanted to be (the clothes fitting looser again). Which meant I didn't succumb to the craving. I don't count calories, I'm just eating 'clean' foods at home and cutting out sugar/caffeine/alcohol for the most part. For me, it was a 'go hard or go home' shake up, and internalizing this as a reset on lifestyle choices. For you, it could be preparing yourself on a non-work day, ready for taking foods to work with you and knowing what you're having for dinner that night.
Years ago I was weight-training at a gym where they trained bodybuilders. While that's not why I was going personally, there was a woman who was a nurse and competing (and won). I was amazed how she did it and with the prep involved with food and her shifts. It came down to discipline and knowing what was driving her to keep with it.
Know what your motivation is. Know what habits you need to change. Then action.