Great source of protein and very filling. Yum!
Place lentils in a bowl of water to soak while preparing the other ingredients. This step is not necessary, but it removes any debris and shortens the cooking time.
Add can of diced tomatoes and carton of broth to a large soup pot. Place over medium heat on stove. Dice celery and onions. Add these to the tomatoes/broth with salt, pepper, and parsley.
Rinse and drain the lentils. Add lentils to the simmering (not boiling) pot. Cook for about 45 minutes, then add frozen mixed vegetables. Let simmer for another 15 minutes.
For a totally vegetarian or Lenten meal, use vegetable broth instead of beef broth. Do not overcook the lentils as they'll become mushy. I estimate that a 1 cup serving has 0 WW points.