Preheat oven to 350 degrees. Line large sheet pan with parchment.
In a medium skillet heat cooking oil over medium heat. Add in diced veggies. Season with 1/4 tsp of salt & black pepper. Stir for a few minutes until tender. Stir in minced garlic and cook one more minute. Place cooked veggies into medium bowl.
To the medium bowl of veggies add ground beef, 1 egg, dijon mustard, 1/4 tsp salt, 1/4 tsp black pepper, 1/4 tsp garlic powder, and 1/4 tsp onion powder. Mix well to combine.
On a clean work surface sprinkle on 1 TBS flour. On fold one thawed puff pastry onto floured work surface. Sprinkle flour on top of pastry. Roll out puff pastry to double it's size, keeping the square shape.
Divide mixture into 4 equal parts . Place each part on to the center of each puff pastry square leaving a 1 inch border.
Bring up all sides of pastry up over the mixture and seal any edges and the top to form a "dumpling" shape. Whisk an egg in a small bowl and brush the egg where all points met at the top.
Place wellington on the prepared sheet pan seam side down. Brush egg on all surface of the pastry. Using a sharp knife cut a slit 2 times on the top of pastry to create a plus sign. Prepare remaining wellingtons and place on sheet pan.
Bake in preheated oven for 1 hour until golden brown on all sides. Garnish with sprigs of fresh thyme. Let rest for a few minutes and enjoy. We love these with mashed potatoes and gravy, and a side of my smashed brussels sprouts. All recipes can be found by searching in my recipe blog catherinesplates.com
NOTE: you can half this recipe to make 2. Also you can mix and match any of the above veggies. These keep the Wellingtons nice and moist.