I too love to use cumin in my lentils... I had a great lentil chili recipe... i will have to look for it for you!
I am not sure exactly but this may be it
1 (16 ounce) package dry lentils
1can tomato paste
2 (14.5 ounce) can petite diced tomatoes
water to cover- unsure how much, maybe keep an eye and add more if needed?
3tbs chili powder(more or less to taste)
1tbs cumin
1/4tsp paprika
1tsp ground red pepper
salt
pepper
some shredded carrots and finely chopped celery, green pepper and onion a couple garlic cloves minced
other veggies can be added if so desired. packed with flavor and I love it! I would adjust your recipe according to your personal preferences- I love spicy so you may need to tone it down or up a bit!~