Fill up a medium pot with water and a pinch of salt. Bring that to a boil.
While the water is coming up to temp, prepare your dressing by mincing the dill and red onion. You will want to have a minimum of 2 tbsp dill and 3 tbsp red onion, adjusting of course based on your preference.
In a mason jar or container with a lid, add the olive oil, vinegar, mustard, dill, red onion, salt, and pepper to taste. Screw on the lid, then give everything a vigorous shake.
During this time, keep an eye on your water. Once it boils, carefully add your peas to the water and cover with a lid. Boil your peas until they are tender.
Once the peas are ready, strain them in a colander and run cool water over them to stop the cooking process. Drain them well, giving them a little pat to get off as much water as you can.
Add them to a large bowl, then, giving your dressing one last shake, add the dressing to the peas. Don't add it all at once - go slowly until you have the amount you like.
Stir well, then chill for at least an hour before serving.