In a medium stainless-steel or enamel saucepan combine strawberries and vinegar. Bring to boiling; reduce heat. Simmer, uncovered, for 3 minutes. Remove from heat. Pour the vinegar-berry mixture through a fine-mesh strainer; let the liquid drain into a bowl. Discard the berries. Transfer vinegar to a jar or bottle. Cover tightly with a nonmetallic lid (or cover with plastic wrap and tightly seal with a metal lid). Chill for at least one hour.
In a medium saucepan cook peas, covered, in a small amount of boiling salted water for 3 minutes. Drain and cool. Arrange peas, spinach, baby Swiss chard, and green onions in rows in a large platter or in a serving bowl.
In a screw-top jar combine 1/4 cup of the vinegar-berry mixture and salad oil. Cover; shake well. Drizzle over salad. Store any remaining dressing in the refrigerator.