This looks like junk food, but it isn't, really, although it combines three economical fast food recipes: the old US diner favourite, 'tomato surprise', 'eggy breads', and what used to be the highly indigestible 'cheese dreams', that fried cheese sandwich that soaked up its weight in lard ... shudder. I think you will find this tomato surprise sandwich much more digestible; in fact if you use a minimum of oil and choose a good bread, it's actually quite nutritious, but could still tempt faddy teens/children. It tempts faddy me!
If you're making several sandwiches, they'll keep warm on a baking tray in a very low oven while you fry the rest. They may crisp up a bit.
If liked, you could spread a bit of hot sauce, ketchup or tomato or onion relish on the bread before adding the cheese.
For a good succulent filling knife-and-fork meal you could top the sandwich with baked beans and a fried or poached egg. Still fast, but ticks all the boxes for protein, fibre, calcium, vitamin C and the like.