Preheat the oven to 400°F (200°C) and line a baking sheet with parchment paper.
Slice each eggplant in half lengthwise. Carefully scoop out most of the flesh, leaving about a ½-inch border around the edges to create sturdy eggplant boats. Chop the removed flesh and set it aside.
Brush the eggplant halves with olive oil and season with salt and black pepper. Arrange them cut-side up on the prepared baking sheet and bake for 20 minutes until they begin to soften.
Meanwhile, heat the olive oil in a large skillet over medium heat. Add the onion and cook for about 5 minutes until softened.
Stir in the garlic and chopped eggplant flesh. Cook for another 5 to 7 minutes until the eggplant becomes tender.
Mix in the tomato paste, vegetable broth, soy sauce, balsamic vinegar, oregano, smoked paprika, onion powder, and crushed red pepper flakes. Stir well and simmer for 3 to 4 minutes.
Add the diced tomatoes and cooked lentils. Cook for another 4 to 5 minutes until the filling thickens slightly. Stir in the parsley and season with salt and pepper to taste.
Reduce the oven temperature to 350°F (175°C).
Fill each roasted eggplant half generously with the lentil mixture. Sprinkle the vegan mozzarella evenly over the top.
Return the stuffed eggplants to the oven and bake for 10 to 15 minutes, until the cheese has melted and the eggplant is completely tender.
Let rest for 5 minutes before serving. Garnish with fresh basil or parsley.