Before starting, preheat the oven to 450°F. Wash and dry all produce. Roughly chop parsley. Drain, then roughly chop olives. Halve tomatoes. Cut cucumber in half lengthwise, then into 1/4-inch half-moons. Peel, then cut half the onion into 1/4-inch pieces (whole onion for 4 ppl).

Stir together 1/2 tbsp oil and 1/4 tsp sugar (dbl both for 4 ppl) in a medium bowl. Add olives, half the parsley and half the onions. Season with salt and pepper, then stir to combine. Set aside.

Stir together mayo, feta and remaining parsley in a small bowl. Season with pepper. Set aside.

Heat a large non-stick pan over medium heat. While pan heats, combine beef, 1/4 tsp salt (dbl for 4 ppl) in a medium bowl. Season with pepper. Form mixture into 2 equal-sized patties (4 patties for 4 ppl). Lightly press a thumb print halfway into each patty. (NOTE: Don't push all the way through!) Add 1/2 tbsp oil (dbl for 4 ppl), then patties to the hot pan. Pan-fry until cooked through, 4-5 min per side.

While patties cook, whisk together vinegar, 1 tbsp oil and 1/4 tsp sugar (dbl for 4 ppl) in a large bowl. Add tomatoes, cucumbers, spinach and remaining onions. Season with salt and pepper, then toss to coat. Set aside.

Halve buns, then arrange on a baking sheet, cut-side up. Toast in the top of the oven until lightly golden, 2-3 min. Spread feta mayo over bottom buns. Top with patties, some dressed spinach leaves, olive tapenade and top buns. Divide burgers and salad between plates.