Bring three cups of water to a boil in a medium saucepan. Add the lentils and 2 teaspoons salt. (Much of the salt will be drained with the water after cooking but will provide added flavor to the lentils.) Stir, reduce heat to low to medium-low, and allow the lentils to simmer, uncovered, for 11 minutes or until cooked but still a little firm. I recommend taste testing. You want them cooked but not mushy. Drain thoroughly.
Return the lentils to the pot in which you cooked them. If they are still a little wet, turn the burner on for a minute, stirring until the lentils are almost dry. Add 1/4 cup of the dressing to the warm lentils and toss. Stir in the greens, tomatoes, scallions, and feta. Toss until thoroughly combined, adding another drizzle of the dressing if desired.
Serve warm or at room temperature. If you prefer the salad warm, you may make the salad up to two hours in advance, allow to sit at room temperature, and gently re-warm for a few minutes on the stovetop in the pot in which you prepared it. Refrigerate any leftovers. They are delicious the next day.