Heat a large skillet (frying pan) on medium high heat. When hot, drizzle with 2 tablespoons of olive oil, along with the onions, and garlic and stir until softened, 2 -3 minutes. Add the mushrooms and 1 teaspoon of salt and cook, stirring often, until the mushrooms have softened and the water has cooked out; the mushrooms should be starting to stick to the pan, 7 - 10 minutes (the time will depend upon the type of mushrooms you use). Add the shawarma spice and toss to coat.
Meanwhile prepare an 8.5 inch (21.5cm) by 4.5 inch (11.5cm) x 2.75 inch (7cm) loaf pan to by drizzling with a little olive oil and swirling it around so it coats the base and sides. Line with parchment paper.
Preheat oven to 375˚F / 190˚C.
Transfer the mushrooms to a large bowl, making sure to scrape off any bits stuck to the pan. Add the carrots, breadcrumbs, herbs, cheese, eggs (or flax eggs), and season with 1 teaspoon of salt and lots of pepper. Mix well. Taste and make sure you’re happy with seasoning, adding more salt or pepper as needed. Transfer the mixture into the prepared tin and press the mixture down to remove as much air as possible.
Bake until the top is golden, and it feels firm and springs back when pressed, about 45 minutes.
Meanwhile, make the tahini sauce. Place the tahini into a small bowl. Add the lemon juice and stir. Add 2 to 3 tablespoons of water, a little at a time, until the tahini is smooth and thin enough to drizzle. Season well with sea salt and black pepper.
Remove the loaf from the oven and set aside to cool for 20-30 minutes (if you slice it too soon, it may fall apart). Cover the pan with a plate or board and carefully invert the loaf. Pour the tahini drizzle all over the loaf and top with herbs and pomegranate. Using a serrated knife, cut into thick slices and serve as is, with a side salad, roasted vegetables or as part of a feast.