Step 1To make the dressing, combine the vinegar, sugar and shallots in a bowl. Slowly beat in the olive oil. Season with salt and pepper to taste. (Makes three-fourths cup.)
Step 2Cook the lentils in boiling salted water until tender but not mushy, about 25 to 30 minutes. Drain and set aside.
Step 3Place the tomatoes in boiling water for 30 seconds, remove and plunge them into an ice bath for a few minutes. Peel, seed and chop.
Step 4Heat a medium skillet and add the bacon. Cook until the fat has rendered and the bacon is crisp, about 10 minutes.
Step 5In a large bowl, combine the lentils, tomatoes, bacon and walnuts. Add one-half to three-fourths cup sherry vinaigrette and stir to combine. Sprinkle with green onions.