Heat a medium size skillet over medium heat. Add the sliced almonds to the pan and toast until golden brown, stirring frequently. When the almonds are done, remove them to a small plate and allow to cool. Wipe out skillet with dry cloth and return to stove.
Heat 1 1 /2 tablespoons of olive oil in skillet over medium high heat. Add breadcrumbs and toast, stirring frequently, until they are golden brown. Add the minced garlic and cornichons and cook 1 more minute. Remove from heat and stir in mustard, parsley, and half of lemon zest. Set skillet aside.
For the beans
Meanwhile, preheat oven to 400 degrees F. Line a large (13 in X 18 in) cookie sheet with aluminum foil. Place cookie sheet in oven and allow to heat up for 10 minutes.
In a medium bowl, toss the green beans with 2 tablespoons of olive oil . Season the beans with salt and freshly ground black pepper.
Remove hot cookie sheet from oven and carefully transfer beans to pan. Spread beans out so that all are in contact with bottom of pan. Return to oven and bake for 6 minutes. Stir the green beans and return to the oven to bake for an additional 4 minutes.
Remove green beans from oven. Squeeze juice from 1/2 lemon onto beans and stir well.
Place skillet of crumb mixture in oven to warm up for 2 minutes. Transfer the beans to a serving dish. Remove skillet from oven. Top beans with warm crumb mixture. Sprinkle almonds and remaining lemon zest over. Serve.
Notes
Adapted from a recipe in Diana Henry's From the Oven to the TableAlmonds can be roasted up to two days ahead. Cover and store at room temperature. Roasted crumb topping can be made up to two hours ahead. Set aside at room temperature.