I used to have this issue, but I solved it with meditation (sort of). This does sound extreme, but it worked for me - even though I was going to the gym every single weekday, I still felt like shit most of the time because of the junk food eating habit I had on the weekends (like you) and I decided enough was enough. Whenever I felt the urge to eat junkfood, I simply meditated. The first few weekends it was really fucking weird… in my mind I was thinking “I’m hungry, why am the fuck am I meditating…”, but after a while my desire to eat junkfood really just plummeted, aswell as an overall increase in energy allowing me to cook something better.
This was honestly really extreme and I do not know how I actually pulled it off without ‘relapsing’. It is not necessary, and I only recommend it if it’s a serious issue for you, which it was for me (and judging by your explanation, it is not a big issue).
Another method I used is what TMPM calls snack city (youtube video) where it’s healthy junkfood. So muffin bites, fries, chicken, etc, all pre-cooked on a single day, then stored in a freezer with easy heatups via a microwave, oven or airfryer, with low-calorie and high-protein focus.
tl;dr I meditated like crazy and stalled my junk food addiction. Easy way to replace junkfood is with ‘healthy’ junkfood -> video - easy and fast meal prep that will last you more than a day. Well worth it.