Make the sauce: heat the grapeseed oil in a small saucepan over medium heat. Add the grated onion and garlic and saute until very fragrant, about 1 minute. Add the ketchup, vinegar, sriracha, maple syrup and worcestershire sauce to the pot and stir to combine. Bring mixture to a light boil, stirring here and there. Simmer until mixture thickens slightly, about 7-10 minutes. Remove from the heat and set aside (leftover sauce will keep for one week in the fridge in a sealed, non-reactive container).

Line a baking sheet with parchment paper and set aside. Place the tempeh pieces and sliced sweet potatoes in a medium-large saucepan. Cover with water by about an inch and simmer until sweet potatoes are soft, about 7-8 minutes. Carefully remove tempeh and sweet potatoes to a plate. Pat dry with a kitchen towel. Place tempeh and sweet potatoes on lined baking sheet.

Heat your barbecue to medium-high or set your oven to broil. Brush tempeh and sweet potatoes with barebecue sauce. Place under the broiler or onto the barbecue. Flip and baste with sauce every minute or so, until coated to your liking and there's a bit of char on the outside.

Place warm tempeh and sweet potatoes on to bread of your choice with desired toppings. Enjoy!