Preheat the oven to 180°C/fan 160°C/gas 4 and line a baking tray with baking paper.

To make the patties, whisk chia seeds and water together and set aside for 3-5 minutes to thicken.

Heat a non-stick frypan over medium heat and saute mushrooms, onion and garlic for a few minutes. Transfer to a food processor with remaining burger ingredients, except flour. Add chia egg, season with salt and pepper and blend until smooth. Gradually add flour to reach desired consistency and refrigerate for 10 minutes. Once mixture is firm, shape into patties, transfer to baking tray and bake for 20 minutes.

To make the spicy smashed avocado, mash ingredients in a small bowl with a fork, adjust seasoning and set aside.

In another small bowl toss tomato salsa ingredients together and set aside.

Layer bottom half of the buns with patties, add smashed avocado and tomato salsa. Top with coriander, lettuce and burger bun to serve.