Preheat the oven to 350°.
Heat a pan over medium-high heat and add olive oil.
Remove the stem from the Portobello mushroom cap and add to the pan.
Also add one thick onion ring alongside the mushroom, at least cut to ½".
Cook the onion ring and mushroom for 2 minutes on each side.
Place the onion ring on top; inside of the mushroom cap.
Add garlic cloves with skins on to pan. Transfer the onion and mushroom to the oven and bake for 10 minutes.
Heat a saucepan with water, filling near the top (leaving about ¼" from the rim). Heat to medium-high.
In the meantime, cut off the large stem from the collard green. Slice avocado, chop onion (1 tbsp), and chives (1 tbsp).
Once the water is near boiling, transfer the collard green leaf to the saucepan.
Cook for 2 min each side, using tongs to lift the leaf easily.
Once the collard green is cooked, drain water and pat dry on both sides.
Place the collard green on a plate. The inside of the leaf should face up.
Remove burger from the oven and set aside.
Drain mushroom caps - they get juicy in the oven! You can also bbq them instead. Pat caps dry and set aside.
Leave garlic cloves in pan and cook for another 20 minutes.
Mix mayo, onion powder, chopped chives, salt, and pepper together.
Once garlic is cooked, remove skins and mince. Add to mayo mixture and stir.
Layer on your garlic mayo to your collard green leaf.
Place the mushroom and onion burger in the center of the leaf.
Add desired sauerkraut (be sure to remove excess liquid), avocado slices and sprouts.
Fold the leaf in four parts, to fully wrap the burger and flip the tucked side over.
Slice it down the middle. Be sure to grab napkins, it will be juicy!