Place the frozen veggies into a bowl and set aside to defrost, about 15 minutes.
Preheat the oven to 190°C/375°F.
Transfer the defrosted veggies into the blender, together with the cannellini beans, onion, coriander, parsley, flour, cumin, cayenne, salt and pepper, and pulse to obtain a rough paste.
Add the sesame and sunflower seeds, and pulse again to incorporate.
Shape the mixture into four burgers using your palms, cover with a plastic foil and freeze them for 10 minutes, then transfer into the refrigerator. (the last steps are important for keeping them firm).
Cut the beet and sweet potato into thin slices using a mandolin, place them on a baked sheet, drizzle with coconut oil and vinegar, season with salt and toss to coat evenly. (you can separate the sweet potato from the beet to avoid the pink coloring of the last one).
Bake for 15 minutes until crispy, then remove and set aside to cool.
Add the spring onions, garlic clove, chickpeas, sun-dried tomatoes, Dijon and lemon juice into the blender, and process to combine, then gradually add the olive oil until you obtain the mayonnaise consistence.
Spray a cast-iron skillet with coconut oil, add the burgers and cook over low heat for 5 minutes on each side, until golden.
In a medium bowl add the arugula, spinach and dill, drizzle with extra olive oil and lime juice, and mix to combine.
Cut a burger bun into halves and toast them for a few minutes on a hot griddle pan or under the grill
Spread some mayonnaise on a burger bun base, add a vegan burger, top with another bit of mayonnaise, then layer 3-4 beet and sweet potato chips, 1 slice of pickled cucumber and fresh greens salad, close with the bun top, then continue the same with the other burgers.
Serve warm or pack to go.