Heat one tablespoon of olive oil in a large pot over medium heat. Add the diced onion and minced garlic. Cook until the onion softens.
Stir in the cumin and chili powder. Add the rinsed lentils, diced tomatoes, and vegetable broth. Bring to a simmer and cook for 25 minutes until the lentils are tender.
While the stew simmers, brush the corn and green pepper halves with the remaining olive oil. Grill them over medium heat for about 8 minutes, turning once, until lightly charred. Cut the corn kernels off the cobs and chop the peppers.
Once the lentils finish cooking, stir in the lime juice and half the chopped cilantro. Season with salt and black pepper. Ladle the stew into bowls and top with the grilled corn, grilled peppers, and remaining cilantro.