Lentil Soup - Madrid Style

Here's a really healthy soup. And it's actually good! Another bonus is it's easy to make.
I got this recipe from Amy years ago. The picture might not look too tasty, but you gotta try it. Lentil Soup Madrid Style

1 large onion
3 carrots
1 green bell pepper
4 Tbsp olive oil
2 Tbsp flour
1 28 oz. can diced tomatoes
2 cups dry lentils
1 Tbsp salt
8 cups water

Dice onion and bell pepper, chop carrot. Simmer vegetables in oil until onions are translucent. Add flour and stir. Add remaining ingredients and simmer (covered) for 45 minutes.