Begin by finely chopping the onion and mincing the garlic, then set aside.
Heat a large skillet over medium heat and add the olive oil. Once shimmering, add the onion and garlic and cook for about 5 minutes until fragrant and translucent, stirring often.
Add the sliced mushrooms to the skillet and cook for another 8 minutes, stirring occasionally, until they soften, release their juices, and turn a deep, earthy brown. Season lightly with salt and pepper.
Meanwhile, rinse the lentils thoroughly and add them to a pot with the vegetable broth. Bring to a boil, then reduce heat and simmer for 20-25 minutes until tender but not mushy. Drain any excess liquid.
Once the mushrooms are cooked, transfer the mixture to a blender or food processor and pulse a few times until roughly chopped, leaving some texture. Let cool slightly.
Mix the flaxseed meal with water in a small bowl and let sit for 5 minutes until thickened into a gel.
In a large mixing bowl, combine the cooked lentils, sautéed mushrooms, flaxseed gel, breadcrumbs, soy sauce, and smoked paprika. Use a spatula to fold everything together until well combined and cohesive.
Transfer the mixture into a greased or parchment-lined loaf pan. Press down firmly to pack it evenly and smooth the top with the spatula.
Bake in a preheated oven at 180°C (350°F) for 40-45 minutes, until the top turns golden brown and the loaf is firm to the touch. Cover with foil if the edges brown too quickly.
Remove the loaf from the oven and let it rest in the pan for at least 10 minutes to set. This helps it slice cleanly and retain its moist interior.
Gently invert the loaf onto a cutting board or wire rack and slice with a serrated knife. Serve warm or at room temperature with your favorite sides, such as mustard or a fresh salad.
