Cook 2 slices chopped bacon in a saucepan; remove with a slotted spoon. Add 2 chopped celery stalks, 2 minced garlic cloves and 1 chopped red onion; saute 4 minutes. Add 4 cups water and 1 cup dried green lentils (rinsed and picked over); simmer until tender, 30 minutes. Stir in 3 tablespoons olive oil, 2 tablespoons sherry vinegar and 1 tablespoon grainy mustard; season with salt and pepper. Top with the bacon, chopped parsley and chopped roasted red peppers.