I don't cook. I'm now married with kids and my husband cooks.
In my single 20s, I went out to dinner probably twice a week. Besides that, I ate:
Kraft Mac & cheese
chicken nuggets
plain pasta with melted cheese on top
cereal
Pasta-roni
Chicken quesadillas - made with cut up chicken nuggets in the microwave. I still make this for my kids for lunch sometimes, ha.
Lots of frozen stuff - Dumplings, hot pockets, chicken wings, frozen waffles, frozen pizza, there was this frozen shrimp scampi I used to like where you just put it in a frying pan for like 3 minutes and then dump on pasta and it was actually really good. I'd cycle through whatever looked easy and good in the frozen food aisle.
If I was feeling really ambitious, I'd make shake 'n bake chicken. You could also buy these pre seasoned, fresh white fish filets that came with specific instructions (put on a cookie sheet in the oven at this many degrees for this many minutes). That was as fancy as I got.
It was a lot of pasta/carbs, so I always made sure I had lots of protein when I was out to eat, and I watched my portions. I also ate a daily green smoothie with lots of spinach and kale (still do) and TONS of fresh fruit and raw veggies, at every meal. In general, yes, I ate a lot of processed stuff, but I had a pretty healthy diet beyond that, watched my portions, and was at a healthy weight throughout that time.