1. Preheat oven to 425°F (220°C). Line a baking sheet with Gefen Parchment Paper.
2. Slice the eggplant into 1/2-inch rounds, and place 10 of the widest slices on a baking sheet in a single layer. Brush with olive oil and sprinkle with salt and pepper.
3. Flip the eggplant slices over and repeat on the second side. Place in oven and bake for 25–30 minutes, until soft. Remove from oven and set aside, allowing to cool slightly.
4. Lower oven heat to 400°F (200°C).
5. Line two baking pans with parchment paper. Remove the puff pastry squares from the package and roll out each square until almost doubled in size. Smear a teaspoon of barbecue sauce in the center of each square in a circular shape, about the size of a hamburger patty.
6. Place a slice of cooked eggplant on top of the sauce on each square. Smear an additional teaspoon of sauce on top of it. Top each eggplant slice with a defrosted onion cube, spreading to cover.
7. Smear each hamburger patty lightly with barbecue sauce on both sides and place on top of the onions on each puff pastry square. Fold each corner of dough over the patty so they overlap each other. Pinch the additional dough over the patty to completely cover and create a circular shape. Place seam side down on a baking pan lined with parchment paper. Repeat until all the puff pastry and hamburgers are finished.
8. Brush the puff pastry circles with beaten egg and top with dried minced onion. Place baking pans in oven and lower heat to 350°F (175°C). Bake for 30 minutes.
9. Drain any accumulated juices out of the pan. Let the Wellingtons rest for three to five minutes and serve hot.