Place lentils in a medium sized pot with ginger, garlic, dried chilies, curry leaves, ground turmeric, and 2 cups water. Bring to a boil.
Season with salt, reduce heat and let it simmer for about 20 minutes until dhal is soft.
Remove from heat. Using an immersion blender, pulse several times to desired consistency.
Heat a skillet over medium heat. Add mustard seeds. When they start to brown or crackle, add cumin seeds and onion. Saute until onion is slightly brown, about 3 minutes, adding water if necessary to prevent burning.
Add jalapeno peppers and tomatoes. Cook for 2 to 3 minutes.
Transfer spices and onions to the pot with cooked dhal. Place pot back onto stove and cook for 5 minutes. Turn off heat.