1. In a large saucepan, saute the onions, green peppers, and celery in heated oil over medium heat for 5 minutes.
2. Add in the water; bring to a boil.
3. Stir in the lentils; cover, lower heat, and simmer 40 minutes (do not drain).
4. Transfer lentil mixture to a large bowl; add in cooked rice, tomato paste, taco seasoning mix, and chili powder; stir to combine.
5. Transfer mixture to a lightly greased medium-sized casserole dish.
6. Bake, uncovered, in a 350° oven for 20 minutes.
7. Sprinkle tortilla chips and cheese on top.
8. Bake another 5 minutes or until cheese melts.