Add lentils and water to a pot (make sure it's high enough to prevent overflow). Bring to a boil, reduce heat to LOW, cover, and simmer until lentils are tender but not mushy. Stir occasionally.
Cooking time for red lentils: 5-7 minutes / yellow lentils: 20-25 minutes.
Combine 1/4 to 1/2 cup cooked lentils with add-ins of choice. Suggestions below to help get you started.
If you want to thin it out, add water, breastmilk/formula, or unsweetened full-fat milk of choice (you can use cow's milk in recipes. Just don't offer as a drink). If it's too soft/mushy, add more lentils and/or ground nuts/seeds.
Serve in a bowl and allow baby to eat with their hands, preload onto a spoon, or shape into balls (refrigerate for at least 30 minutes. The balls will firm up and hold shape better).
Cook a large batch of lentils to keep in the fridge for up to 5 days or the freezer for up to 1 month. I recommend freezing in 1/4-1/2 cup containers (I like to use the tray above) so you can easily pull out single-serving portions and add all kinds of fun mix-ins.
Once you add in the other ingredients, start by offering a small portion to your baby. You can always offer more as you follow your baby's lead. That way you can store untouched leftovers in the fridge for up to 3 days.