Step 1

Whisk the eggs, feta, milk, 1/2 teaspoon salt, and 1/4 teaspoon pepper in a large bowl to combine; set aside.

Step 2

Heat the oil in a large nonstick frying pan or seasoned cast iron skillet over medium heat until shimmering. Add the onion, season with salt, and cook, stirring occasionally, until softened, about 5 minutes. Add the spinach, tossing continually, until completely wilted and any liquid has evaporated, about 3 minutes.

Step 3

Reduce the heat to medium-low and pour in the egg mixture. Let sit undisturbed until the eggs just start to set around the edges, 1 to 2 minutes. Using a rubber spatula, push the set eggs from the edges into the center. Spread the uncooked eggs back into an even layer. Repeat, pushing the set eggs from the edges into the center every 30 seconds until almost set, for a total cooking time of about 5 to 6 minutes. (The top of the eggs should still be slightly wet.)

Step 4

Remove the pan from the heat and fold in the tomatoes. Serve immediately with toast or toasted pita bread.