Rinse and drain the lentils. Place them in a large pot covered with about 2 inches (5 cm) of water and bring to a boil. Season with salt. Simmer over gentle heat, uncovered, for 20 to 25 minutes, until the lentils are tender but al dente. As they simmer, skim the foam from the surface. Drain and cool.

In a large salad bowl, combine the lentils with the diced tomato, pepper, onion, scallion, and garlic. Toss to combine. Add olive oil and vinegar and toss again. Taste and adjust seasoning with additional salt if necessary. Garnish with parsley and hard-boiled eggs and serve immediately.