Dry toast the walnuts or pumpkin seeds in a frying pan, then set aside.
Season the pigeon fillets with salt and pepper. Heat the oil in the same frying pan, add the herbs and garlic, then cook for 30 seconds. Add the pigeon steaks, sear them on both sides. Cook for 5 minutes, turning them every minute. Add the port, let it sizzle and reduce the jus completely. Move the pigeon steaks onto a plate and let them rest.
Meanwhile, scatter the lettuce leaves into 4 serving plates. Cut the beetroots into thin wedges, the tomatoes into halves or small pieces. Arrange these on top of the lettuce.
Slice the steaks into thin pieces, arrange these on top of the salad, then scatter the walnuts/pumpkin seeds on top. Drizzle each plate with olive oil and balsamic vinegar, just before serving.