Season the flank steak generously with salt and pepper on both sides.
Grill the steak over medium-high heat for approximately 4-5 minutes per side until it reaches your desired level of doneness.
Transfer the steak to a cutting board and let it rest for at least 5 minutes before slicing thinly against the grain.
Place the egg in a small pot of boiling water and cook for 7 minutes for a jammy yolk, then immediately transfer to an ice bath, peel, and slice in half.
In a small jar or bowl, whisk together the olive oil, lemon juice, raw sugar, salt, and pepper to create the vinaigrette.
Arrange the mixed greens, sliced cucumbers, and radishes in a large serving bowl.
Top the vegetables with the sliced steak and the soft-boiled egg halves.
Drizzle the lemon vinaigrette over the entire salad just before serving.