Stovetop: Preheat dutch oven or heavy bottom medium pot on low-medium heat and swirl oil to coat. Add onion and garlic, cook until golden brown (5 minutes), stirring occasionally. Add turmeric, coriander, curry powder, cumin and salt; cook for another 30 seconds, stirring frequently.
Add coconut milk, tomato paste, water, lentils and stir to combine. Bring to a boil, cover and cook on low for 45 minutes. Remove from heat and let stand 5 minutes.
Slow Cooker: Preheat small skillet on low-medium heat and swirl oil to coat. Add onion and garlic, cook until golden brown (5 minutes), stirring occasionally. Add turmeric, coriander, curry powder, cumin and salt; cook for another 30 seconds, stirring frequently.
Transfer to a slow cooker and add coconut milk, tomato paste, water and green lentils. Stir to combine, cover and cook on High for at least 3 – 4 hours or on Low for 6 – 8 hours.
Instant Pot: In Instant Pot, add ingredients in exact same order: onion, garlic, turmeric, coriander, curry powder, cumin, salt, green lentils, water, coconut milk and tomato paste. Do not stir!
Cover, set pressure valve to Sealing and press Pressure Cooking on High for 25 minutes. After do Quick Release to release the pressure by turning the valve to Venting.