Preheat oven to 350 degrees F. Cook the rice according to the package instructions and dice the chicken, and slice the lemons and onion.
Layer the rice on the bottom on a small baking dish. Arrange the diced chicken over the rice.
In a small bowl, mix the chicken broth and tomato paste until well combined.
Pour the sauce over the chicken. Sprinkle the paprika and celery seed over the chicken. Top with the lemon slices and onion.
Cover the casserole with aluminum foil and bake in the preheated oven for 55 minutes. Check halfway through baking and if seems too dry then add in a little more chicken broth.
When done, uncover the casserole dish and broil for 2-3 minutes, just until browned and bubbly.
Notes
Chicken thighs can be substituted.
Store leftover casserole in an airtight container for 1-2 days in the refrigerator.