Directions

Cooking the Potato Filling
Rinse the potatoes then peel. Slice the potatoes into 1/8" pieces. Discard the peels.
Slice the onions into 1/8" strips.
Cut the tomato into 1/4" thick slices.
Preheat a medium frying pan (10") with 1/4 cup extra-virgen olive oil to medium low.
Add the potatoes and stir to cover in olive oil. Cook for 10 minutes stirring regularly so that the potatoes cook evenly.
Next add the sliced onions to the potatoes. Cook for 5 more minutes stirring continually so that the potatoes and onion cook evenly and don't burn.

Add the oregano and cook for 5 more minutes stirring continually. Don't allow the mixture to brown.
Remove the potato onion mixture from the heat and strain. Allow to cool for 10 minutes. Reserve the olive oil. You will use it to cook the omelette.
While the potato onion mixture is cooling. Cook the sliced tomato in the same pan over medium heat. Turning once, cook the tomato until it is just starting to brown and set aside.