Rinse and drain both the lentils and chickpeas separately. Add 1/2 the lentils along with all the chickpeas to the bowl of a food processor. Add in the garlic, herbs, whole chilli, chilli flakes, cumin, turmeric and lime juice, season well with salt and freshly ground black pepper. Whizz until blended and smooth but still with a little texture. Turn out into a large mixing bowl.
Add the remaining lentils, pumpkin seeds and oats. Using clean hands, combine all together well then using slightly damp hands, shape into 4 patties. Place on a tray, cover with cling film and chill in the fridge for a few hours or overnight, if possible.
To make the salsa; cut the pineapple and avocado into 1cm cubes, add to a bowl and cover with the lime juice. Add the onion and mint and chia seeds if using. Season with a good pinch of crushed sea salt flakes and a dash of freshly ground black pepper. Stir to combine. Cover and set aside.
To cook the burgers, heat a little extra virgin olive oil in a large non-stick frying pan set over low-medium heat. Cook burgers 2 at a time turning only when the first side is golden brown. Very carefully turn over and continue to cook for approx. 20 mins until firm and browned.
To serve, lightly toast the burger buns, spread a little mayo on the top of the bottom half, add lettuce, the burger, tomato slices, then top with the salsa and a splash of hot sauce if using. Serve any extra salsa alongside and a wedge of lime.
Try not to turn the burgers more than 2-3 times as even though you want them to cook evenly, they can break apart due to the nature of their ingredients. Slow and steady frying over low-medium heat is the key here.