Warm your pan over medium-low heat for about a minute. Add the oil and let it warm for another minute.
Add your finely diced onion and tomato, stirring occasionally until softened, about 5–7 minutes. Make sure both vegetables are diced into small pieces so they cook evenly and incorporate into the eggs without leaving large chunks.
Beat your 2 eggs in a separate bowl with a fork or whisk. If the pan feels too hot, reduce the heat slightly. Pour the beaten eggs into your pan along with the sea salt.
Let the eggs sit undisturbed for a few seconds until you notice the edges beginning to set. Using a spatula, gently push the cooked eggs from the edges toward the center of the pan, allowing the uncooked egg to flow into the empty spaces.
Continue gently pushing and folding the eggs every few seconds until soft, fluffy curds form and the eggs are mostly set but still slightly glossy. Remove from the heat immediately, as they'll continue cooking from the residual heat.
Serve warm with arepas or toast.