You can make some Tortilla Española very delicious. There are other variations that are simpler. Just look up tortilla for recipes. You can add onions in there too.
You can add some suggars to your diet too.
Alternatives:
Bread and cheese sandwich. Bread and jelly sandwich. Tortilla with some chicken in there. Chicken omlette.
Cook eggs in all kinds of ways possible, like omette, plat, poached, japanese style, souflé ... Mashed potatoes, cooked potatoes. Fried potates, roasted potatoes; roasted potatoes with chess filling. Roasted potatoes with egg and cheese filling.
You could of course add other vegetables like tomates and onions. A moroccan salad could help you change a bit. This salad could be reduced to only two ingredients.
As much as you really can gain weigt with potatoes and bread, you need to add some proteins. Like lentils, very cheap, or just a little bit of chicken to spice it up.
One important thing is to eat more than once a day. If you really need to gain weight fast, eat at least 3 times a day. Bread and scrambeled eggs in the morning. Torrtilla for lunch, and some other kind for dinner. and a cheese sandwich for 18:00.