Heat oil in a medium-sized sauté pan over high heat. When hot, add onions, carrots, potatoes and red peppers. Lower heat and sauté for 3 minutes or until just soft. Remove from heat.
Pour lentils into deep saucepan. Add water, stock and vegetables. Add dill, salt and pepper. Place over medium heat and cook, stirring frequently, for 45 minutes or until lentils are soft but not mushy. When done, remove from heat and stir in cooked meat or poultry, if desired. Serve hot.