It isn't really necessary to put anything in with lentils when cooking them except for water; however, adding seasoning to the cooking liquid can give your lentils an extra layer of flavor. Lentils are versatile legumes featured in the foods of various regions. The best seasonings to add to your lentils will depend on the type of cuisine you are cooking.
The classic Indian dish dal is made by cooking lentils with seasonings such as cumin, turmeric, coriander and cardamom. For a quick version, you can simply add the powdered spices to the lentils' cooking liquid. For deeper flavor, toast whole spices in a dry pan on medium-low heat, shaking the pan to keep them from burning. Once the spices are toasted, add them to the cooking lentils. Add about 1/2 teaspoon of salt for each cup of dried lentils while they are cooking.
To season lentils with traditional Egyptian flavors, add chopped garlic while they are cooking, as well as ground cumin, spearmint and parsley. Dried mint and parsley work well, and fresh mint and parsley provide even deeper flavor. Add 1/2 teaspoon salt for each cup of dried lentils.
For traditional Italian flavor, add chopped garlic while the lentils are cooking, as well as fresh or dried basil and fresh or dried oregano. Use more basil than oregano, because the oregano tends to overpower basil. Add a few tablespoons of dried fennel, if desired. Put in 1/2 teaspoon salt for each cup of dried lentils.
To season lentils with classic Greek flavors, add chopped garlic while they are cooking. Sprinkle on dried or fresh oregano and spearmint, as well as fresh lemon juice when they are almost soft. Use about 1/2 teaspoon salt for each cup of dried lentils.