Gather all ingredients, rinse lentils, and chop onion.

Layer lentils at the bottom of the crockpot, followed by onions, tomatoes, and chili powder.

Pour vegetable broth over the mixture until the lentils are covered.

Set the crockpot to low and cover, cooking for 6 to 8 hours.

Check lentils for tenderness and adjust cooking time as necessary.

Serve hot in bowls and add optional toppings before serving.