Well, whatever you eat at dinner time could be considered dinner. A tube of pringles followed by a pack of smarties if you like.
But on the basis that I would consider "dinner" to be the main, most substantial meal of the day, I don't think simply an omelette or a jacket potato would cut it. I'd want at least 2 -3 portions of veg contained within my main meal, and for it to be substantial enough to fulfil a good chunk of my calorie requirements for the day.
I'd consider a 2 egg cheese omelette served with a large mixed salad/ a variety of veg and chips or new potatoes as a reasonable main meal
I'd consider a jacket pot with butter on the side of meat /fish (or other protein) plus a variety of veg as a reasonable main meal.
I'd consider a large jacket potato with a generous topping of homemade chilli or similar served with a large mixed salad as a meal.
A simple omelette alone, or a simple jacket with cheese isn't substantial enough or nutritious enough to serve as the main meal of the day. Obviously as a one off - fine, but not routinely.
If DH was regularly serving up a simple omelette or jacket pot in the place of a full dinner on his days to cook, I'd consider him a lazy sod that was taking shortcuts and not providing a proper meal. But that would be on the basis that on my days I provide home cooked, nutritionally balanced full meals, and my expectation would be that he put the same effort in on his days. If every day of his was a shortcut "cheat" day, he'd be pushing the full responsibility of providing an adequate nutritionally balanced diet firmly onto me.