Start with soaking the oats in sufficient water. This step is not necessary but I feel like it cuts down the cooking time substantially. You can soak them for the duration when the recipe calls for them, so 5-6 minutes. If you soak them longer, the oats might get soggy.
Set a heavy bottomed pan on medium high heat and add olive oil to it. Once the oil is hot and shiny, add the mustard seeds and curry leaves. Stand back as the curry leaves might splutter and mustard seeds will start to pop.
After about 30 seconds, add the onions (if using), carrots and peas and cook for about 5 to 6 minutes.
Drain the oats and add to the pan along with turmeric powder and salt. Add about 1.5 cups of water. If you like your oats a bit mushy, you can add 2 cups water. Mix well. Once the water starts to boil, lower the heat and cook, uncovered for about 8-9 minutes or until the oats are tender. Keep stirring in between.
Taste and adjust salt if needed. Squeeze the lime juice in, garnish with chopped cilantro and serve warm.