Heat olive oil in frying pan over medium heat. Add leeks and sea salt and stir occasionally, cooking until crisp, about 2 minutes. Don’t burn. Remove from heat, and drain oil into a small bowl.
Add red wine vinegar to oil and whisk with a fork to blend. If not already toasted, toast hazelnuts in a pan on the stove or in a toaster oven at high heat for a couple minutes. Be careful not to burn! Roughly chop.
Assemble salad, layering leaves with apples, crumbled chèvre, and chopped hazelnuts. Drizzle with dressing mixture. Add a few sprinkles of sea salt, to taste.