Preheat the oven to 375°F (190°C) and line a large baking sheet with parchment paper.
Cut the eggplants in half lengthwise. Using a sharp knife (a small paring knife is best), cut a ½ inch (~1.25 cm) border around the inside, being careful not to pierce all the way through the eggplant.
Make deep vertical and horizontal cuts within the border you made, again, being careful not to cut all the way through the eggplant.
Use a spoon to scoop and scrape out the eggplant flesh into a large bowl.
Place the hollowed out eggplant halves onto the prepared baking sheet and brush the insides with a generous amount of olive oil. Season with a sprinkle of salt and pepper.
Flip the eggplants over so they're cut side down then bake for 30-35 minutes until softened.
Meanwhile, heat 1 tbsp of olive oil in a large pan over medium heat. Add the onions and sauté until translucent. Add the garlic and toss until fragrant, about 30 seconds.
Add the ground lamb and break it up with a wooden spoon. Cook until the meat has browned.
Add the harissa, tomato paste, cumin, paprika, coriander, salt, pepper, and lemon juice. Stir to combine then stir in the beef broth (or water).
Add the cubed eggplant and break up any large chunks. Toss to coat in the sauce then reduce the heat to medium-low. Tamp the eggplant down with the back of a spoon to create a flat layer in the pan (this helps with even cooking).
Stir and flatten occasionally until the eggplant has softened and the sauce has significantly thickened, about 30 minutes.
Mash the softened eggplant into the sauce then taste and add more salt if needed.
Turn off the heat then stuff the hollowed out eggplants with the lamb filling.
Serve with a dollop of Greek yogurt and chopped parsley.