Pre-heat the oven to 400 degrees F. Place the asparagus spears on a roasting tray or baking sheet in one layer. Sprinkle both the olive and sesame oil on the asparagus and toss with your hands or a spatula. Sprinkle on the sesame seeds, salt and pepper. Roast in the oven for 15-20 minutes or until the asparagus is very lightly browned and the tips are a little crispy. Add the lemon zest and squeeze the lemon juice onto the spears. Garnish the asparagus with lemon slices and serve.