Heat a large skillet over medium heat. Add the bacon and cook until browned and crisp on both sides, 4-6 minutes. Remove the bacon and add the green beans and spring onion. Sauté until the beans are just crisp tender and the onions are slightly browned, 3-5 minutes. Remove the beans and onion and set aside.
Tear lettuce onto a large platter and season with salt and pepper. Dress the lettuce with dressing to taste and toss to combine. Add the sliced radish, hardboiled egg, green beans, onions, crumbled bacon, and feta cheese. Dizzle with more dressing and serve immediately.
For the dressing
In a large container, combine all of the dressing ingredients. Blend together using an immersion blender or countertop blender until smooth. Taste and adjust for seasoning.