Set Instant Pot to sauté mode.
Add cumin and mustard seeds and toast for ~30 seconds.
Add garlic, ginger, and chilli. Cook for another 30 seconds.
Stir in tomatoes and ground spices.
Simmer for about 5 minutes, stirring and scraping the base.
Turn off sauté. Add water and stir the base clean.
Add mung beans and mix well.
Seal lid and cook on High Pressure for 10 minutes.
Allow natural pressure release (~20 minutes).
Open lid and stir in coconut milk, coriander, and lime juice.
Simmer briefly if needed, then taste and adjust seasoning.