In a large skillet, heat 1 tablespoon olive oil over medium heat. Add the sliced onions, peppers, and jalapeno, sprinkle over the sugar, season with salt and pepper, and sauté for about 8 to 10 minutes until fairly tender. Transfer to a plate, and scrape out the skillet.
Return the skillet over medium high heat. Add the tablespoon of oil, then the mushrooms and garlic. Season with salt and pepper, and sauté for 10 minutes until the liquid has evaporated and the mushrooms have turned nicely browned. Stir in the thyme for the last minute of cooking. Turn onto another plate, scraping out the pan.
Return the skillet to medium heat, and when it’s hot add the last tablespoon of olive oil and the diced onion. Sauté for about 8 minutes until tender, but don’t let it get more than golden brown. Add the greens and sauté for another 4 or 5 minutes until they are wilted and tender. Turn the greens onto a third plate.
Stuff the vegetables into the buns. See the recipe intro for advice about adding cheese, which I wish I had done.
Notes
Want to add cheese? I would use provolone or Muenster or Monterey Jack, tuck the slices around the filling, and warm the whole thing on a baking sheet in a preheated 375° oven for about 4 minutes, until the cheese got melty.Or leave out the cheese altogether for a vegan sub sandwich.