Heat the olive oil in a large pan and grill the steaks on both sides until done to your liking. Remove and set aside to rest.
Use a vegetable peeler to shave long thin ribbons from the length of the cucumber. Place the ribbons into a bowl and add the chopped herbs, sliced onion, chili, and lemongrass.
Add the fish sauce and a pinch of sweetener. Squeeze over the lime juice and add a dash more fish sauce for saltiness if needed. Drizzle over a little olive oil and toss well to coat. Divide between two bowls.
Slice the steak against the grain and serve on top of the salad. Enjoy your Thai Beef Salad!