Before starting, preheat broiler to high. Wash and dry all produce. Core, then cut apple into matchsticks. Cut brie in half, through the centre, parallel to the cutting board. Halve buns. Whisk together vinegar, half the fig jam and 1 tbsp oil (dbl for 4 ppl) in a large bowl. Add apples and toss to combine. Peel, then cut the onion into 1/4-inch slices.

Heat a large non-stick pan over medium heat. When hot, add 1 tbsp oil (dbl for 4 ppl), then onions. Cook until slightly softened, 3-4 min. Add remaining fig jam and season with salt. Cook, stirring occasionally, until the onions are dark golden-brown, 4-6 min. Carefully rinse and wipe pan clean.

Arrange halved buns on a baking sheet, cut side up. Spread mustard on bottom buns and top with brie halves, cut-sides up. Spread onion mixture onto top buns. Broil in the middle of the oven, until brie melts, 3-5 min.

While sandwiches toast, heat the same pan (from step 2) over medium. Heat over medium heat. Add the pepitas to the dry pan. Toast, stirring often, until golden-brown, 3-4 min. (TIP: Keep your eye on them so they don't burn!) Transfer to a plate.

Add arugula and spinach mixture and pepitas to the large bowl with apples and dressing. Toss to combine. Season with salt and pepper.

Sandwich top and bottom buns together, then cut in half. Divide sandwiches and salad between plates.