Rinse the millet in a sieve and drain. 1⁄4 l Bring salted water to the boil in a pot. Stir in the millet. Cover and simmer for about 10 minutes, then let it swell for another 10 minutes.
Meanwhile wash and quarter the tomatoes. Clean, wash and shake dry the arugula. Pluck the mozzarella into pieces. Loosen millet with a fork if necessary. Whisk eggs and season with salt. Bake 2 omelettes one after the other, but heat 1 teaspoon of oil in a small coated pan (22 cm Ø). Add half the egg mixture. Spread about 2 tablespoons of cooked millet and half of mozzarella on top. Cover and let it simmer at medium heat for about 4 minutes. Keep the finished omelette warm in a hot oven (electric cooker: 100 °C/circulating air: 80 °C/gas: see manufacturer) and bake the 2nd omelette in the same way.
Put omelettes on plates. Arrange arugula and tomatoes on top. Sprinkle with remaining millet and season with some pepper.