Cut daikon into 2-3 inch pieces. Cut pork into 3-4 inch pieces if not already cut. Cut tomatoes into fourths. Slice onions to your preference.
Combine tomatoes, onions, daikon, meat and water in the Instant Pot. Push the Pressure button (or Manual button if you have an older model), set timer to 30 minutes and make sure pressure valve is closed.
Once pressure cooking is finished, press the Cancel button and open valve to release pressure.
With the Instant Pot lid open, push the Sauté button and bring water to a boil.
Gently mix in lemon juice and salt (to taste). The tomatoes should start to separate and disperse while you mix.
Add any other vegetables to the Instant Pot. Once vegetables are cooked to your preference, gently mix the soup and set the Instant Pot to Warm.