Summarize:

You may have some or most of the ingredients that you will need. The necessary ingredients are pretty basic, which makes this an easy and cost-effective soup to make. You'll want both the garlic and onion to be finely chopped. This is a tedious process, but it can be done while you're waiting for the lentils and chicken stock to boil. Put the pot over the stove on medium to high heat. Once the lentils and stock begin to boil (the liquid makes big bubbles), lower the heat to a simmer. The lentils will be done when they are soft and rise to the top of the liquid. Cook until the water comes out of them (the onions will begin to look transparent), but don't put the heat on so high that they brown because this will alter the taste of your soup. If you're not a fan of cayenne pepper, salt and black pepper will work fine on their own. Stir and do a taste test. If it needs more spices, add them to the broth. After a couple of minutes of letting all the ingredients combine in the pot, add the lemon juice. Let the juice mingle with the soup. After a couple of minutes of letting the lemon juice infuse through the soup, the soup will be ready to eat.
Check your refrigerator and pantry. Peel and cut up the garlic and onion. Add the lentils and chicken or vegetable stock to the pot. Combine the chopped onion and garlic with some olive oil (a little goes a long way). Add spices to taste. When the garlic and onion are fully cooked, transfer them from the pan into the pot with the lentils and chicken or vegetable stock. Cut the lemon in half and squeeze the juice. Serve.