Prep the basics: Rinse the lentils under cold water until the water runs mostly clear. Peel and cube the sweet potatoes.
Dice the onion, mince the garlic, and grate the ginger.
Sweat the aromatics: In a large pot, heat the oil over medium. Add the onion with a pinch of salt and cook 4–5 minutes until translucent. Stir in garlic and ginger and cook 30–60 seconds until fragrant.
Toast the spices: Add cumin, smoked paprika, turmeric, cinnamon, and red pepper flakes.
Stir for 30 seconds to bloom the spices. This step deepens flavor.
Build the base: Add the chopped bell pepper (if using), diced tomatoes with their juices, sweet potatoes, and lentils. Stir well to coat everything in the spices.
Add liquid and simmer: Pour in the vegetable broth.
Bring to a gentle boil, then reduce to a simmer. Cover slightly ajar and cook 25–30 minutes, stirring occasionally, until lentils are tender and sweet potatoes are soft but not falling apart.
Adjust texture: If it looks too thick, add a splash of broth or water. If you want it creamier, mash a few sweet potato chunks against the pot wall and stir them in.
Finish with greens: Stir in the spinach or kale and cook 2–3 minutes until wilted.
Taste and season with salt and pepper.
Brighten it up: Turn off the heat and stir in lemon juice or vinegar. That little bit of acidity makes the flavors pop.
Serve: Spoon into bowls over brown rice or quinoa, or serve with warm flatbread. Top with fresh herbs and a dollop of yogurt or tahini if you like.