While ribs are in oven, place a medium pan over medium heat. Add 1 Tbsp. olive oil into hot pan, then add sliced onions and a pinch of salt and pepper. Cook for 3-5 minutes until onions begin to get tender. Add 1/4 cup water, 1 Tbsp. apple cider vinegar, turn the heat to high, and bring to a boil. Add collard greens, reduce heat to medium, cover, and allow to simmer for about 15 minutes. Season with salt, pepper, and Tabasco sauce to taste (reserve some for garnish, if desired.) Set aside.