Preheat an oven to 400 degrees, and position an oven rack in the center. Place a baking sheet in the oven to heat.
Use a pestle and mortar to crush the rosemary, lavender, herbs de Provence and lemon zest. Add the oil to the mortar and mix until combined with the herb mixture.
Place the flank steak in a shallow non-reactive dish and, using a paring knife, make 1/4-inch slits in the flesh and then pour the marinade over. Turn the steak to thoroughly coat both sides, pressing the spices onto the steak. Cover and marinate for 30 minutes.
Preheat a grill pan to medium-high heat. Add 1 tablespoon olive oil to the pan, heat through until the oil is shimmering.
Remove the steak from the marinade and season with salt and pepper. Place the steak on the prepared grill pan and cook 2 to 3 per side or until you can see grill marks on both sides. Take the steak off the grill and place onto the baking pan in the oven. Bake the flank steak until desired doneness, until the internal temperature reaches 135 degrees, about 8 to 10 minutes.
Transfer the steak to a cutting board, tent with aluminum foil; allow to rest for at least 5 to 10 minutes.
To serve: Slice the meat against the grain; squeeze fresh lemon over the top and serve now or later.
Preheat oven to 400 degrees. In the bowl of a food processor, pulse bread until fine crumbs form. Transfer to a medium bowl; add ground beef and ground pork.
Place onion, garlic, celery, carrots and parsley in food processor; pulse until finely chopped. Add to beef mixture; combine using your hands. Add egg, 1/2 cup ketchup, 2 teaspoons dry mustard, salt and pepper; combine thoroughly, using your hands. Place in an 8 1/2-by-4 1/2-by-2 1/2-inch loaf pan.
In a small bowl, combine the remaining 1/4 cup ketchup and 2 teaspoons dry mustard, and the brown sugar; stir until smooth.
Brush mixture over top of the meatloaf. Place the pan on a baking sheet to catch drippings, and transfer to oven. Bake until a meat thermometer inserted in the center reaches 160 degrees, about 1 1/2 hours. (If the top of the meatloaf gets too dark, cover with foil and continue baking.) Let meatloaf stand 15 minutes before slicing.