Heat oil in large pot over medium; cook onion 5 minutes until soft and translucent.
Add garlic, cumin, paprika, and cayenne; stir constantly 1 minute until fragrant, preventing burning.
Mix in rinsed lentils, tomatoes with juices, broth, and carrots.
Boil; reduce to low and simmer uncovered 25-30 minutes, stirring occasionally, until lentils tender and stew thickened.
Cook spinach 2-3 minutes until wilted; season with salt and pepper.
Serve hot with cilantro, lemon squeeze, and crusty bread for dipping.