In a small food processor, pulse the shiitakes into a fine mince. Add the roasted vegetables and pulse until the mixture is about the same size as the shiitakes. Do not pureé! Transfer to a mixing bowl and combine with the napa cabbage, chives, ginger, and tamari or soy sauce.
To prepare the potstickers, have a small bowl of water, your filling, and a tablespoon nearby, as well as wonton wrappers and a large parchment-lined baking sheet.
Place 3 wrappers on the baking sheet. Scoop 1 tablespoon of the filling into the center of each wrapper. Dab water around the edge of the wrapper with your finger. Fold one side of the wrapper over the filling to create a half moon shape, then grab the edges and bring them to the top, while creating a flat bottom on the dumpling by gently pressing down on the filling. Pinch-pleat the edges at the top down to the bottom corners to seal. Slightly turn the corners inward. Repeat with the remaining filling and wrappers. At this point, you can freeze the sheet, and once the potstickers are frozen, transfer them to a freezer-safe container or bag. If you have leftover wrappers, you can freeze them also. Thaw in the fridge before using.
When ready to cook the potstickers, place the sesame seeds on a small plate. Bring a pot of water to boil and cook 6 to 8 potstickers at a time in the boiling water, until they start to float to the top, about 2 minutes. If boiling from frozen, boil for 3 to 4 minutes. With a slotted spoon, transfer the dumplings to a baking sheet or large plate.
Meanwhile, heat a large, nonstick pan over medium heat with 1 teaspoon of the oil. Using a pair of tongs to hold the potsticker, place the flat bottom side into the plate of sesame seeds, generously coating it. Place the sesame seed side down into the hot pan and fry for about 4 minutes. You can turn the potstickers onto one side and fry for another 30 seconds to 1 minute if you feel the seam needs to be cooked and steamed a little. Fry in batches of 5 or 6 depending on how large your pan is, adding 1 teaspoon oil per batch.
Serve immediately with sesame soy vinaigrette on the side for dipping.