Pre heat the oven to 180 degrees C / 356 F, I use an electric, fan assisted oven please adjust according to your own oven.
Heat the oil in a skillet and cook the onions over a low to medium heat for 15 minutes, stirring occasionally, they should be golden brown and soft when cooked.
Add the potatoes to the onions, then the spinach, cook until the spinach starts to wilt. Turn of the heat.
Add 3/4s of the cheese, salt and pepper to the eggs and mix.
Pour the egg mixture over the spinach and potatoes and stir a little.
Place the tomatoes on top then sprinkle over the remaining goat's cheese.
Place on the middle shelf of the oven and cook for 15 minutes, until the eggs are cooked.
Serve warm or cold with a green salad.