If not already cut, slice the bacon into relatively thin slices. Peel the outer layer off the spring onions and trim the end. Cut the white and light green part into slices. If using pearl onions, peel and cut in half or quarters, depending on size.
Warm the butter in a small pan/pot with a lid over a medium-high heat. Add the bacon and cook a couple minutes, stirring regularly, but don't let it brown. Add the onion and cook a minute more to gently soften the onion.
Add the peas and stock, cover the pan with the lid and reduce the heat to a simmer. Leave the peas to cook for around 10-15 minutes so that the liquid absorbs and the peas are cooked through. If the liquid is gone quickly, add a little more.
Once the peas are cooked, add the salt, pepper and sugar and stir through. Tear the lettuce leaves and place over the top of the peas, cover with the lid again and cook another minutes.
Stir through and serve.
Video
Notes
Ideally, use fresh peas for this. If you have peas in their shell, you will need roughly twice the weight before shelling, so around 8oz/225g. If fresh are not available, you can use frozen, just cook for a little less time.