Bring a medium pot of water to a boil. Add frozen peas and cook 60–90 seconds until tender-crisp. Drain and plunge into ice water to stop cooking. Drain well.
Whisk together mayonnaise, sour cream (or Greek yogurt), apple cider vinegar, Dijon mustard, and sugar. Season with salt and pepper to taste.
In a large bowl combine peas, diced onion, shredded cheddar (if using), and chopped bacon (if using). Pour dressing over salad and fold gently to coat evenly.
Cover and chill for at least 30 minutes, ideally 2–4 hours. Taste before serving and adjust seasoning. Garnish with fresh herbs.
Notes
Make-ahead: Keeps up to 3 days refrigerated in an airtight container. Stir in a teaspoon of milk if dressing firms up.
Vegetarian: Omit bacon or use a smoked crumbly cheese for smoky flavor.
Texture tip: Blanch frozen peas briefly for best color and snap; avoid overcooking.
Variations: Add feta and lemon zest, or swap cheddar for goat cheese.