In a medium pot, combine lentils, chicken broth and salt. Bring to a boil, reduce heat to low, cover and simmer for 20 minutes. Set aside.
Meanwhile, preheat large skillet on high heat and add oil. Add chicken, cumin, taco seasoning, salt, pepper and cook for 6-7 minutes, draining liquid into a large bowl halfway through and stirring occasionally. Transfer chicken to same large bowl and set aside.
Preheat oven to 375 degrees F. Return skillet to medium-high heat and add oil. Add onion, garlic, bell peppers, taco seasoning, cumin, salt and cook for 5-7 minutes or until golden brown, stirring occasionally.
Transfer to the bowl with chicken along with cooked lentils, diced tomatoes, corn, 1/2 cup cheese, diced green chilies, taco seasoning and 1/2 cup cilantro. Mix gently with spatula enough to combine.
Transfer mixture to a 9 x 13 ovenproof baking dish and level/press gently with spatula. Bake uncovered for 30 minutes. Sprinkle with remaining cheese and bake for another 10 minutes.
Remove casserole from the oven, cover with foil and let stand for 30 minutes before serving.
Garnish with remaining cilantro, cut into 8 slices and serve hot.
Notes
Store: Refrigerate in an airtight container for up to 3 days.
Freeze: In an airtight container up to 3 months.
Meal prep: Assemble, tightly wrap with plastic and then foil, and freeze for up to 3 months. Thaw in the fridge overnight and bake as per instructions plus 5 minutes.