In a food processor, pulse the lentils, walnuts and mushrooms together until combined but still textured — you want it to hold together, not turn into a paste.
Transfer to a bowl and mix in the tomato paste, soy sauce, garlic and spices. Season well with salt and pepper.
Divide into 4 portions and roll into loose balls. Heat a large skillet over medium-high heat with the olive oil.
Place a tortilla in the pan, then set a ball of mince on top. Immediately press down hard with a spatula to smash it flat and thin, right into the tortilla.
Cook for 2–3 minutes until the edges crisp and caramelise, then flip the whole thing (mince-side down) and cook for another 1–2 minutes.
Top with cheese and spring onion while still hot so the cheese melts slightly, then fold, finish with coleslaw, parsley and a drizzle of BBQ sauce, and serve immediately.