This is how my mom makes mergimekli chorba (lentil soup)

1 cup red lentils,cleaned from small stones and impurties (but maybe your lentils don’t need this step) and well rinsed.
1 potato, grossly diced
1 carrot, grossly diced
1 zucchini, grossly diced
1 large onion, chopped
some garlic (4-5 cloves)
Bouillon (I guess about 8 cups)
salt and black pepper

Boil everything together until lentils and vegtables are very soft.
Blend (easiest with a hand blender) and serve, sprinkled with ground cumin.
As an extra treat, you can fry some flat pita pieces in oil until golden, and serve with the soup (sprinkle it on each bowl just before eating).

There is also this version, which is maybe more Lebanese, but also very good. It is Lentil soup with Siliq (swiss chard)
Here you use brown lentils.

1 cup brown lentils, picked and rinsed
2 big handfuls siliq rinsed and coaresly chopped
1 large onion
5-6 cloves garlic, finely chopped
1 handful fresh coriander (cilantro), finely chopped
Juice of ½ or whole lemon

Bring the lentils to a boil
Add the swiss chard
Fry the onion in some olive oil until wilted. Add to the soup.
Gently fry the garlic nd coriander (heavenly smell). Add to the soup.
When the lentils are done, add lemon juive, cumin, salt and pepper to taste.

Bon apetit!