Add chopped onion, celery, carrot, garlic, ginger to a large pot over medium heat for 5 minutes, stirring occasionally. If it begins to stick add small splashes of water and keep stirring. Stir in red curry paste until combined and fragrant, about 1 minute.
Rinse and drain lentils. Add lentils and water to pot and stir. Bring to a low boil, then reduce heat to a simmer and cover for 10-12 minutes until lentils are cooked and vegetables are soft.
Meanwhile, Cook rice noodles according to package instructions in a separate pot. AND in a small bowl, whisk together tamari, miso paste, coconut sugar, tahini and sriracha (if using) until smooth. Add mixture to soup and stir to combine.
Blend soup until smooth - You can use an immersion blender or allow soup to cool, then use a standing blender and return to pot. Bring back to a low simmer.
Add thinly sliced red peppers and spinach. Cover and simmer for 3 minutes or until peppers slightly soften and spinach is wilted.
Remove from heat and stir in lime juice and cooked rice noodles. Adjust salt, pepper and lime to taste and enjoy with any additional toppings of your choice!