Spread asparagus in a single layer on a large rimmed baking sheet. Brush with olive oil until spears are completely coated.
Sprinkle asparagus with 1/4 teaspoon salt and place in the oven. Roast for 10 to 12 minutes, depending on the thickness of the asparagus.
Meanwhile, melt butter in a small sauce pan over medium heat. Continue cooking until the butter is golden brown and has a nutty aroma, about 3 to 4 minutes.
Remove the butter from the heat and cool slightly. Add the harissa and mix it into the butter using the back of a fork. Mix until there are no lumps left.
Tip the panko and 1/4 teaspoon of salt into the harissa butter and stir until the breadcrumbs are completely coated.
Remove asparagus from the oven and squeeze the lemon over the top. Toss gently with a pair of tongs.
Preheat the oven to broil. Arrange the asparagus with the tips together in an OVEN SAFE serving dish (i.e: Pyrex, enamelware or stoneware). Line the asparagus up and spoon the seasoned panko over the top, heaping it down the middle of the asparagus.
Place the oven safe dish under the broiler and watch for the breadcrumbs to turn slightly golden, about 1 minute.
Remove from oven and serve asparagus at once.
Notes
This dish needs to be enjoyed immediately, while the breadcrumbs are still crisp. One they grow cold, they are no more appealing than stale toast. However, the dish can be assembled in advance, held and room temperature for up to 30 minutes and then broiled just before serving.