I will also eat the same foods for breakfast and lunch, sometimes for years on end.

You wouldn't happen to be neurodivergent, would you? Food hyperfixation is super common in folks with ADHD and/or autism; eg. I've been eating salads for a couple of months straight 😅 There's variation between them but usually the base is boiled whole grain barley, different greens (but almost always including spinach), bell pepper, cucumber, scallion, maybe some sprouts, some vinaigrette, and then this absolutely lovely mirin-marinated tofu you can get from stores here