Lightly coat sweet potatoes with oil and a pinch of salt and pepper. Spread out on a sheet pan and roast until tender, about 15-18 minutes. Set aside.
Heat 2 Tbs olive oil in a soup pot over medium high heat. Add onion and cook until golden brown. Add garlic and cook for 30 seconds. Add sherry and reduce by half. Add tomatoes and mushrooms, and simmer for 15 minutes.
Add a pinch of salt and pepper, barley and about 3 quarts of water. Bring to a boil and then down to a simmer. Cook for 20 min.
Add collards and escarole and cook until tender, about 8-10 minutes.
Remove from heat, stir in sage and sweet potatoes. Adjust seasoning with salt and pepper.