In a large bowl, combine the juice pulp, onion, garlic, oregano, cumin, salt, chili powder, egg and breadcrumbs until well incorporated. The mixture should stay together when squeezed. If it's too wet, or is falling apart, try mixing in a bit more breadcrumbs as needed. Portion out into 6 equal mounds, and then shape into patties using your hands. Place on a baking sheet or plate and continue shaping each one.
Place a griddle pan over medium-high heat. Once hot, grease with 1 tablespoon coconut oil and fry 3 patties at a time. Cook for about 2 to 4 minutes on the first side, or until golden brown, and then flip over and cook for 1 to 2 minutes longer. Return to plate. Grease the griddle once more with the remaining coconut oil and cook the remaining 3 patties in the same way.
To assemble the burgers, split the buns open, and toast, then spread with mayo or mustard if you wish and fill with a patty, lettuce and slice of tomato. Sandwich together and serve immediately.