Heat a large Dutch oven or other large soup pot over medium heat and add 1 tablespoon oil, or enough to coat.
Once hot, add the onion and a small pinch of salt and sauté until softened, about 5-7 minutes, stirring occasionally.
Add the garlic, ginger, and jalapeños and continue cooking until fragrant, stirring occasionally, for 1 more minute.
Add in the ground spices (curry powder, garam masala, cumin, coriander, turmeric, ground mustard) and cook until fragrant, stirring frequently, about 30-60 more seconds.
Add the carrots and stir them to coat.
Add the crushed tomatoes, coconut milk, and vegetable broth and use a spatula to scrape off any browned bits from the bottom of the pot.
Add the red lentils, salt, and some freshly ground black pepper and stir everything to combine.
Bring the mixture to a boil, then reduce the heat to a simmer and cover the pot partially.
Cook until the lentils have fully softened, about 20 minutes, stirring occasionally to prevent any sticking to the bottom of the pot.
Cover the pot all the way in the last 5-10 minutes of cooking if the dal is getting too thick.
Stir in the spinach and cook until slightly wilted, about 1-2 minutes.
Add in the lemon juice and stir once more.
Turn off the heat.
Serve warm with your choice of rice, a dollop of coconut yogurt, and some fresh cilantro.
