In a small bowl, whisk together the tahini, lemon juice, garlic, cumin and a good pinch of sea salt.
Drizzle in the water and whisk until the sauce is smooth and not too thick.
For the sourdough
Preheat the oven on grill. Brush the sourdough slices on both sides with a little olive oil. Season lightly with salt and pepper.
Place the sourdough on a baking tray and grill until both sides are lightly toasted and crisp.
For the main
In a medium sized bowl combine the celery, parsley, mushrooms and vinegar.
Drizzle in a little olive oil and season with salt and pepper. Toss to combine and coat everything well.
Smash the avocado in a small bowl with the cottage cheese and a pinch of salt.
Spread a quarter of the smashed avocado onto each slice of bread. Top with a generous pile of the mushroom and celery salad.
Dollop tahini sauce all over so that each bite of salad toast gets a good amount. Finish with a sprinkle of toasted nuts and seeds for crunch and serve!