In a large pot over medium heat, add the oil, onion, and salt and cook until softened, stirring occasionally, about 3 minutes.
Stir in the tomato paste, ginger, and garlic, and cook, stirring often, for about 1 minute.
Stir in the water, veggies, protein, rice, and soy sauce. Increase the heat to high and bring it up until you start to see little bubbles (we just want to warm everything up). Turn off the heat and transfer 1 cup of liquid to a medium bowl. Add the miso and use a fork to mix/mash until the miso is mostly dissolved. Pour back into the soup and stir in the lemon juice.
You can eat as is or top with sriracha, fresh cilantro or scallions, and/or a soft-boiled or fried egg.