Combine the lentils in a saucepan with the water. Bring to a boil; then cook at a rapid boil for 15 minutes.
Add the rice and tomatoes; then reduce to a simmer. Cook for another 25–30 minutes, or until all liquid is absorbed.
Once cool, fork-mash or purée the meal according to baby's preference. Thin with water, breastmilk, or formula if desired.