Put the lentils in a pot and cook them in lightly salted water according to package instructions, or until soft and fully cooked.
Chop the carrots, mushrooms, onion, celery stalks, walnuts, and red pepper.
Heat some vegan butter in a pan over medium-high heat. Roast the onions and carrots for about 5 minutes, then add the remaining vegetables and walnuts. Cook for another 10 minutes until everything is nicely browned and fragrant. Season generously with salt and pepper.
Drain the cooked lentils through a sieve and let them steam off. If needed, rinse briefly with cold water to cool them slightly. Transfer to a large bowl and add the roasted vegetables, rosemary, thyme, paprika powder, rolled oats, mustard, flax seeds, and finely grated smoked tofu. Stir until well combined.
Generously grease a loaf pan and firmly press the mixture into it, packing it tightly to avoid air pockets. Let the loaf rest in the pan for at least 30 minutes so it can set. Carefully turn it out onto a baking tray. You can loosen the sides with a knife if it doesn't want to separate from the pan.
Bake at 180 °C / 350 °F for about 45 minutes. Remove from the oven and let the loaf rest for 30–60 minutes. You can spread some cranberry or red currant jam on top before serving. Enjoy!