Cook the lentils
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.

Cook the chicken
Heat a large skillet over high heat and add oil. Add chopped chicken, cumin, taco seasoning, salt, and pepper. Cook for 6–7 minutes, stirring occasionally. Drain excess liquid halfway through cooking into a bowl. Transfer cooked chicken to the same bowl.

Prepare vegetables
Preheat oven to 375°F (190°C). Return skillet to medium-high heat and add oil. Add onion, garlic, bell peppers, taco seasoning, cumin, and salt. Cook for 5–7 minutes until softened and fragrant.

Mix casserole filling
Add cooked lentils, vegetables, diced tomatoes, corn, green chilies, taco seasoning, cumin, 1/2 cup cheese, and 1/2 cup cilantro to the bowl with chicken. Stir gently until combined.

Assemble casserole
Transfer mixture to a 9×13-inch baking dish and spread evenly.

Bake
Bake uncovered for 30 minutes.

Add cheese topping
Sprinkle remaining cheese over the casserole and bake another 10 minutes until melted and bubbly.

Rest and serve
Remove from oven, cover with foil, and let rest 30 minutes before slicing. Garnish with remaining cilantro and serve warm.