Slice scallions, separating white and light green parts from dark green parts. In large pot, heat 1 Tbsp. of oil over medium heat. Add white and light green scallion slices and Italian seasoning; cook, stirring, until softened, 3-4 minutes. Add 4 cups water, bouillon cubes, peas, carrots and potatoes. Cover; bring to a boil. Over low heat, cook until vegetables are softened, 5 minutes. Add tortellini; bring to boil. Over medium heat, cook until tortellini and vegetables are tender, 4-5 minutes. Stir in remaining scallion slices.